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University M icrofilms International 300 N. Zeeb Road Ann Arbor, Ml 48106 8426371

Cichan, Michael Anthony

VASCULAR CAMBIUM AND WOOD DEVELOPMENT IN SELECTED CARBONIFEROUS PLANTS

The Ohio State University Ph.D. 1984

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International300 N. Zeeb Road, Ann Arbor, Ml 48106

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University Microfilms International VASCULAR C&flBJUB AID ROOD DEVELOPREHT I » SELECTED

cmmSIFEEQUS FLAWS

DISSERTATION

Presented in Partial Fulfillment of the Requirements for

the degree Doctor of Philosophy in the Graduate

School of The Ohio State University

Hichael Anthony Cichan* B»A-* H-Sc-

* * # # *

The Chio State University

1984

Reading Committee; Approved By

Thomas N„ Taylor

Gary L- Floyd

Daniel J. Crawford

Ralph E- Boecner Thomas N Taylc Department of Botany C opyright by M ichael Anthony Cichan 1984 D U IC 1 U 0 1

®enory of my mother# Cecelia mmoimimsims

I ttould like to thank Dr s. David F® Brauer® Charles a.

Good® G ilbert H® leisraan® and Benton H® Stidd for graceous-

Ij alXo@iag ae to examine their fossil plant collections and providing some of the specimens used in this study® I bouM also like to thank the members of ay reading commit tee for helpful comments on this work. Financial assis tance fro® the Ohio State University Graduate School in the fore of a Graduate Student Alumni fiesearch heard and a Uni v e r s i t y Presidential Fellowship is also gratefully ack n o w l edged. This investigation was c a r r i e d out under the s u p e r v is io n o f Dr® Thomas N. Taylor® whose expertise and enthusiastic manner encouraged and stimulated my interest in the biology of fossil plants. A student c o u ld a sk no more than this of a teacher® and I thank him for his sup port® advice® and friendship® Finally® I would like to extend my deepest appreciation to my wife® Paula® and my children® David and Cecelia® for giving me the love and understanding that was so critical for the completion of this project® fWl

O c to b er 2 8 4 , 195# ...... Born - Philadelphia* Pennsylvania

1978 Bo A. * LnS a H e C ollege* Philadelphia* Pennsylvania

1977 - 1979 ooooooooooooo^oo leaching assistant* Rutgers University* Newark* New Jersey

1978 - 1979 teaching Assistant* Butgers University* New Brunswick* Ken J e r s e y

1979 Ho Sc.* Butgers University* New Brunswick* New Jersey

1980 - 1981 0 ^ 0000.000000000 T each in g A s s is ta n t the Ohio State University* Colum bus* Ohio

1982 - 1983 oooooo

1983 - 198# ...o.o.oooooo.o. Presidential Fellow* The Ohio State University* Columbus* Ohio

Professional Affiliations

Botanical Society of America* Paleobotanical Section Botanical Society o f America* Structural/Developmental Section American Association for the Advancement of Science Palaeontological Society* London International Association of Hood Anatomists International Organization of Paleobotany The Society of the Sigma Si The Ohio Academy o f S c ie n c e The Torrey B o ta n ica l Club Research I n t e r e s t s

Structure and evolution o f the vascular cambium Anatomy and morphology of Carboniferous plants Reproductive biology and evolution of angiosperms Electron microscopy of fossil pollen and spores

A&rards and H onors

1983 The Ohio State University Presidential Fellowship

1983 The Ohio State University Graduate Student Alumni Research Association Award

1983 Isabel Co Cooksoa Award* Paleobotanical Section* Botanical Society -of America* best student paper presented at annual meeting

Extramural Grants

1981 - 1982 Grant for student research* The Geological S o c ie ty of America; Project Title; Characterization of the megafossil flora of the Cranks Creek coal ball locality (Carboniferous) in eastern Kentucky. $600

1983 National Science Foundation Doctoral Dissertation Grant for Research in the F ie ld S c ie n c e s ; Project Title: The structure* organization* and activity of the vascular cambium in Pennsylvanian- age plants. $4060

Service to the Ohio State University

1980 Student representative on the Space and Facilities Committee (Department of Botany)

1981 Member of the Sailer lecture Committee (Department o f Botany)

1982 - 1983 Student representative on th e Colloquium Committee (Department of Botany)

Publications

1979a Parthenocarpy in Cichoriua intvbus. Bot. Sac. Amer. Hisc. Ser. P u b l. 157s 7 . "(M. A. C ichan and B. F. P a ls e r ) .

- v - 1979b Parthenocarpic achenes in Cichoriua iotyfcus L. B u ll, lea Jersey Acad. Sci. 38s 38. ( 8 . A. Cichan and B. P. Falser).

1980 Phylogenetic trees in plant systematics. O hio J. Sci. 80: 22. | f . Steussy, V. Funk* and M. A. Cichan).

1981a Oa th e s t r u c t u r e and morphology of the seed Pachvtesfca m uacii a . sp. (Bedullosales). fie?. Palaeobot. Palynol. 34s 359-367- (fl. A. Cichan and T. H. T a y lo r ).

1981b The application of scanning electron microscopy in the characterization of Carboniferous lycopod wood. Scanning Electron flicrosc. 1981. 3s 197-201. |KU 1. Cichan^ T= I . T a y lo r s and 2. L. Smoot) .

1981c In analysis of cambial development in Sphenophvllum. Chio J. Sci. 81s 29.

1981d Stauropteris in the Carboniferous of North America. B ot. Soc. Amer. fiisc. Ser. Publ. 160s 4 3. |M. A- Cichan and T. N. T a y lo r ) .

1981e The v a scu la r c a ib iu ® in Carboniferous plants: Sphenophylluta. Bot- Soc. Amer. ftisc. Ser. Pull. 160: 4 3 .

1982a Development of seedless and normal achenes in Cichcrium intybus (Compositae). Amer. J. Bot. 69- 885-895. p. A- Cichan and B. F. F a lse r) .

1982b Structurally preserved plants from southeastern K entucky: Stauaropfceris tiseriata sp- nov. Amer. J. Bot. 69: 1491-1496- (H. A- Cichan and T. N. Taylor).

1982c Plant-animal interactions in the Carboniferous: Wood borings in Premnorylon. Palaeogeography, Palaeo- climatology, Palaeoecology 39: 123-127. |M. A. Cichan and T. N. Taylor)-

1982d Vascular cambium development in SphenophyHum, a Carboniferous arthrophyte. IAWA Bull- 3: 155-160. (H. A- Cichan and I. N. Taylor).

1982e Book Beview: Paleobotany, Paleoecology, and Evolution. Volume 1- Karl J. Niklas (ed.). International Organization of Falaeolotany Newsletter #19. 1982f The e a r lie s t-k n o w n arthropod burrows in fossil wood Ohio J® S c i, 82s 17. fff® A® C ich an and T. B. T aylor)

1982g Sood b o rin g s i n Premaozylons Plant-animal interactions i n th e Carboniferous® Bot® Soc® Amer. Misc. Ser® Publ® 161s 56®

1983a A systematic and developmental analysis of Arthropitys deltoides sp. now® B ot. Gaz- 14; 4s 285-294® (H® A. Cichan and T« B® Taylor) ®

1983b Self-fertility in Cichorim intybus 1® Bull. Torrey Bot- Club 170s 316-323®

7 983c A new calaoite from the Carboniferous of eastern Kentucky® Ohio J. Sci® 83s 7 6 ® (H. A® Cichan and T® M® Taylor).

1983d The vascular caobiui in Carboniferous plants; Arthropitys communis® Amer. J. Bot 70(5) , p t . 2; 69®

1984a A method for determining tracheid lengths in p e t r i f i e d wood by analysis of c r o s s s e c t i o n s . Ann. Bot® 53: 219-226® (fl» A. Cichan and T® N® T a y lo r ).

1984b Ultrastructural studies of in situ Deyonian spores: Protobarinophyton Pennsylvaniaua Brauer. Bev. Palaeobot. Palynol. (in press). (H. A. Cichan, T. N® Taylor, and D. F. Brauer).

1984c Camfcial development in the Carboniferous lycopod Paralycopodites brevifolius (Milliamson) DiHichele- Ohio J. Sci- 84: 7.

1984d The ultrastructure of Mesozoic pollen; Pteruchus dubius. Eev® Palaeobot® Palynol. (in press) - (T® B. T a y lo r, i . A® Cichan and A® M. Baldoni)® ia b l b of c o a s i r a s

Fag®

Bedlcatlon ...... l i aeksa©ole

W rta ...... © ....© .....© ....a ® . JLW

List of Tables ...... © ® . . l i

List of Figures ...... • . . „ „ . . . xlw

List of Plates ...... swl

C h a p te r

i . istbodoctiqb ...... i

LEPIDODEEDBALES ...... 7 SPHENQPHYLLALES ...... 12 EQ UISETALES 16 HEDUILGSALES ...... 21 COREALTALES ...... 26

II. S1TEB11LS ABO flETBODS ...... 3®

Specimen Directory ...... 30 Techniques ...... 33 i s Z U . 11S0MS ...... 44

LEPXDODENDBALES ...... 44 Lepidodeadrid Stens 44 S tigm aria 59 SPHEMOPHILLALES ...... 73 EQUISEXALES .91 Arthropitys communis . . . . . 91 Arthropitys deltoides ...... 106 HEDULLOSALES ...... 120 C Q B L AX TALES . . . oooaraoraoraoooo 134

17. DXSCiSSl®! ...... 147

LEPIDO DEHOR ALES » ...... 147 S PH E NO PH II I ALES ...... 158 EQ01SETALES ...... 162 RED ULLOS ALES o . 166 COREAITALES ...... 170 General Discussion ...... 173

¥ . BXBZJOGMMI ...... 184

71. Appendix A ...... 201

fAppendix B ...... 208

¥IU® Appendix C . ... o . . 213

1I0 Appendix 0 ...... 218

I® Appendix E ...... 225

AppendrX .P ...... 228

XXI® Appendix G ...... 233

- ix - LISI Off 21UE5

IfaMe ffage

1® Data—Paralycopodites ...... 201

2® Data-—Paralycopodites ...... 202

3® Data-—Paralycopodites . . . . . 203

4® Data— Paralycopodites ...... 204

5. Data—Paralycopodites ...... 205

6. Data— Paralycopodites ...... 206

7. Data—Paralycopodites ...... 207

8. Da ta — S tig m a r i a ...... 208

9. Data—Stigaaria ...... 209

10. Data—Stigaaria ...... 210

11. Data—Stigaaria ...... 211

12. Data—Stigaaria ...... 212

13. Data— Sphenophyllua ...... 213

14® Data— Sphenophyllua ...... 214

15. Data—Sphenophy Hum ...... 215

16. Data— Sphenophyllua ...... 216

17® Data—Sphenophyllua ...... 217

18. Data-—Arthropi fcys ...... 219

19® Data—Arthropitys ...... 220

20. Data—Arthropitys ...... 221

- x - 21® Data—Arthropitys . • . 222

22® Data—Arthropitys . . 223

23® Data— Arthr opitys . ..«••••. - 224

24® Data—Arthropitys . .. ®®®®®®«»»®®® = 225

25® Data—Arthropitys . . „®®®®®®®®..«o 226

26® D ata— A rth ro p i fcys . . . 227

27® D ata— H ed u llo sa • » 228

28® Data—Hedullosa . . 229

29® Da ta — He d n llo sa » . 230

30® Data—HeduiJLcsa . ». . ® 0«s®ffl®®®«.®®®231

31® Data— Hedullosa . . . .„„® ®« -232

32® Data—Cordaites . . 233

33® Data—Cordaites «- ...... -...---2 34

34® D ata— C o r d a ite s . ® * « 235

35® D ata— C o r d a ite s ...... 236

36® Data—Cordaites . . 237

s i LIST OF FIGUBES

Figare Page

1. Illustration showing method for determining radius of obligue axis in coal tall slal » . 42

2« Diagram of camcial cylinder used in determining number of cells in meristem at r a d iu s 3 » 42

9. Graph showing percent composition of tracheid, ray and leaf trace versus percent wood r a d iu s 53

10. Graph of tracheid length and mean width v e r s u s p e rc e n t wood r a d iu s 53

11. Graph of tracfceid number versus percent wood r a d iu s 55

12. Graph of tracheid number versus percent wood radius for stem exhibiting rone of "subdivisicr” »».„ 55

24. Graph of percent composition versus percent wood r a d iu s 67

2 5 , Graph of mean BT ray area versus percent wood radius . «...... «. «» . . « . «. *■> «• . 67

26. Graph of tracheid length and mean width versus percent wood radius 69

27, Graph of number of tracheids versus percent wood radius . .. . _ » » . . . » „ » «... .. 69

4 4 . Graph of tracheid length and mean width versus percent wood radius 88

45. Graph of number of tracheids versus percent wood r a d iu s 88

4 6 . Standardized stem anatomy in Sphenophyllum .. - 90

- x i i - 51. Graph of percent cexposition of tracheid component and fascicular and interfascicular ray v e rs u s p e rc e n t wood r a d iu s .>••••.••100

52. Graph o f t r a c h e i d le n g th and mean width v e rs u s p e rc e n t wood r a d iu s • ••,•••.... . 100

53. Graph of number of fascicular ray cells and • tracheids versus percent wood radius . .. « 102

54. Graph o f mean f a s c i c u l a r ray c e l l s iz e v e rs u s p e rc e n t wood r a d iu s •••••.,. » . . • 102

69. Graph of percent area of tracheid component and fascicular and interfascicular ray v e rs u s p e rc e n t wood r a d iu s . •»<.•.. 114

70. Graph of interfascicular ray cell size v e rs u s p e rc e n t wood r a d iu s .»....•„„•• 114

71. Graph of number of f a s c i c u l a r and interfascicular ray cells versus percent wood r a d i u s • 116

72. Graph of tracheid length and mean width v e rs u s p e rc e n t wood r a d iu s • •»»•••••.. 116

73. Graph of number of tracheids versus percent wood r a d iu s 118

74. Graph of fascicular ray cell size versus p e rc e n t wood r a d iu s ...... 118

79. Graph of percent composition versus percent wood ra d iu s ...... 129

80. Graph of tracheid length and mean width v e rs u s p e rc e n t wood r a d iu s ..«„••••„•• 129

81. Graph of number of tracheids versus percent wood r a d iu s 131

93. Graph of percent area of tracheid and ray components versus percent wood radius . . - „ • 140

94. Graph of tracheid length and mean width versus percent wood radius ...... 140

95. Graph of number of tracheids versus percent wcod r a d iu s 142

- xiii - 96. Graph of mean ray cell size versus percent vi cod r a dr us 1

97. Graph of number of ray cells versus percent wood radrus . . . . » •> . . . « . . » . « . . . ^

98. C am bial D evelopm ent in T e re te v e rsu s E llrptical Axes » . . .. « . ■■ a* «. •« . . ■ *. . «14S

- xiv - LIS2 OS BLADES

P l a t e P age

I. lepidodendrid stess—Fig. 3-8 ...... 51

II- Lepidodendrid Steis—Pig. 13-17 ...... 57

III. Stig maria—Fig. 18-23' ...... 65

I Vo Stigmaria— Fig* 28-31 ...... 71

Vo -Sphenophyl3.ua-—Fig. 32-37 ...... 84

¥1 o Sphenophyllum— Fig- 38-43 ...... 86

VII- Arthropitys com munis— Fig- 47-50 oo„-»oo 98

VIII- Arthropitys communis—-Fig- 55-61 ...... 104

IX. Arthropitys deltoides— Fig- 62-68 ...... 112

X. Medullosa— Fig. 75-78 ...... 127

XI. hedullosa—Fig. 82-86 ...... 132

XII. Cordaitean Stems— Fig. 87-92 ...... 138

- xv - Chapiter Z

11210D1CSZ0H

The vascular cambium has been defined as "the actively dividing layer of cells that lies between, and gives rise to* the secondary xylem and phloem" (International Associa tion of Hood Anatomists, 1964)-, la contrast to apical meristems, shere the cells are relatively uniform in appear ance, the vascular cambium is characterized by two distinct cell types that correspond to the axial and radial systems in the derivative tissues- Cambial cells that produce tra cheids, vessel elements, fibers, sieve cells, and other elements of the axial system are termed fusiform initials-

In general, these cells are elongate parallel to the long axis of the organ and exhibit tapering end walls- The other cambial component, the ray initials, are much smaller, more or less isodiametric, and produce rays in the wood and phloem- The cells of the cambium divide in a consistent and characteristic manner in forming the secondary vascular tissues- Both fusiform and ray initials divide periclinally producing derivatives (xylem and phloem mother cells) that usually continue to divide periclinally several times. Eventually* these derivatives differentiate and mature in t o the cells of the vascular tissues® Repeated periclinal cell divisions in the cambium and adjacent zones result in the radial alignment of cells in the secondary xylem and phloem® As this process continues and new tissue is formed tOHard the inside of the axis* the cambium is displaced ceatrifugally* thereby enlarging the circumference of the cambial cylinder® This process of cambial enlargement is accommodated by the production of new initials® la gener al* new fusiform initials result from the anticlinal divi sion of preexisting o n e s; the formation of a transverse or pseudo-transverse (oblique) wall accompanies nuclear divi sion forming two new daughter initials® Each new fusiform c e l l i s approximately half the length of the original ini t i a l . Circumferential cam bial expansion occ urs a s a r e s u lt of the subsequent intrusive elongation o f the newly formed cells. In certain specialized angiosperms ( e . g . * Legumino- s a e , Bigncniaceae) * the orientation of the new wall is hor izontal* and the resulting daughter initials are essential ly equal to the mother initial in length. In these storied meristems * circumferential enlargement of the cambium occurs through the subsequent increase in the tangential diam eter of the daughter initials. Sew ray initials are form ed by a variety of mechanisms including transverse sub division of fusiform initials* lateral division of fusiform initials, reduction in size of an individual fusiform ini tial, and horizontal and lateral subdivision of preexisting ray initials®

During development of the axis, the vascular cambium is derived, in part, from the procambial strand, and in part, from cells of the ground tissue (the cortex in stems, the pericycle or cortex in roofs)® She former, which usually begins to develop first, corresponds to the fascicular cam bium® fhe latter, which typically begins to fctm later in development connecting the fascicular portions of the meristem, corresponds to the interfascicular cambium. The fact that the cambium is at least partially derived from the procambial strands has led to the conclusion that the lateral and apical meristerns are spatially and temporally continuous. This general continuity of meristernatic zones has acted to mask the distinction between primary and sec ondary growth, and various workers have suggested alternate criteria to be used in distinguishing the two (Larson,

1982|® for example, it has been proposed that the first occurrence of ray cells (Catesson, 1964), the first evi dence of anticlinal division in the fusiform initials (as determined by an abrupt decrease in the length of the tracheary elements) (Bailey, 1944; Cumbie, 1963) , and the first occurrence of fibers in the wood (Larson and isefc- rands, 1974) be used as structural markers to indicate the 4 onset of secondary growth® lo date a unanimously accepted and universally applicable test to distinguish between pri mary and secondary growth has yet to be proposed {larson*

1982)® Similarly* there has been continuing debate as to whether or not the vascular cambium actually represents a discrete* continuous unilayer of actively dividing ini tials® On the one hand* Catessca |1964* 1974* 1980} and other workers (e.g® * Srivasfcava* 1964) studying the cambium in angiosperms* have maintained that meristematic activity is not localized in a single cell layer but*, rather* is diffuse throughout the cambial zone (i.e.* the narrow band of tissue at the interface between the xylem and phloem mother cells where cell division is occurring at the high est rate) . On the other*, workers who have focused their a t t e n t i o n on gymnosperms ( Bauman* 1955; Neuman* 1955; Mur- manis* 1970) have suggested the occurrence of a single per manent initial in each radial file of the cambial zone.

Ultimately this difference of opinion may be reconciled on the basis of differences between the cambia of major taxo nomic groups (Philipsoa* Hard* and Eutterfield* 1971; Cat esson*, 1974)® Nevertheless* despite the apparently simple construction and mode of action of this meristem* it is clear that there has been considerable difficulty in achieving a precise and universal definition of the vascu lar cambium. Because meristeiatic tissue* in general^ is extremely

fragile* the cells are rarely preserved in fossil plants

(Delevoryas* 1964)„ Thus* in axes that are preserved as

permineralizations (Schopf* 1975) the presence of a vascu

lar cambium is usually inferred on the basis of the pres-

eace of secondary xylenu In this context* important fea

tures for recognizing xjlea as secondary include the radial

organization of the cells and the presence of a ray system-

Since studies of modern plants* hoaewer* have shown that a

moderate degree of radial seriation can occur in primary

xylem (Esau* 1943* 1954; Sterling* 1946* 1947; Sachet*

1954; Parke* 1963; Soh* 1972)* and some woods lack a well-

developed ray component (Barghocrn* 1941; Boureau* 1957;

Carlguist, 1970)* such criteria are not uneguivocal.

Despite the lim itations imposed by imperfect cellular pres ervation* these features continue to be the most useful in suggesting the presence of a vascular cambium in fossil

p l a n t s (S ch eck ler* 1974* 1975)-

The vascular cambium appeared rather early in the evolu tion of vascular plants (Barghoorn* 1964; Banks* 7970*

7981; Tiffney* 1981)* perhaps in response to strong selec

tive pressure for plant height- Ef the middle Devonian* limited secondary growth had developed both in members of

the Aneurophytales - Aneurophvton (Schweitzer and flatten*

1982), Protopteridium (Krausel and tfeyland* 1938; Mustafa* 1975; Schweitzer and Batten* 1982 )0 and Trlloboavion

(Arnold* 1940; Scheckler and Basks* 1971a)* and the Cladox- ylales - Cladoxylon (Mustafa* 1978)* and Xenocladia

(Arnold* 1940* 1952)-=® More extensive amounts of secondary vascular tissues were produced by plants of the late Devo nian* in particular the Aneurophytales - Proteokalon

(Scheckler and Banks* 1971b)* TefcraxvloEteris (Beck^

1957)* the Archaeopteridales - Callixyloa (Arnold* 1930;

Beck* 1953) * and the Sphenophyta - Archaeocalamites

(Seward* 1898).. Although the reasons are not entirely clear* the evolution of a cambium within individual lineag es occurred rather rapidly (Scheckler and Banks* 1971a)* and by the end of the Devonian secondary growth is known to have been present in all of the major plant orders in exis tence at the time (Barghoorn* 1964) „ The trend toward woodiness attained full expression with the development of the Carboniferous coal swamps* which were inhabited by a complex array of plants exhibiting a variety of different growth forms,, Although arborescent plants were by far the most prominent* a well-formed understory was also present

(liffney* 1981)»

* See Scheckler (1974* 1975)* however* for a discussion of secondary growth in the Cladoxylales. 7

LBgIDODjglEBM.ES

Parkaps the most distinctive plants that gres in the Car boniferous peat-forming swamps were the arborescent lycopods. In addition to being the most abundant form in terms of percent vegetation (Phillips and DiMichele, 1981 ) , th e s e plants were probably the tallest elements of the floraj some specimens are known to have been in excess of 35 i tall (Scott, 1920; Arnold 1947; Thomas and Watson* 1976).

In contrast to the stems of modern plants* which derive mechanical strength from the presence of a broad cylinder of secondary xylem* rigidity in lepidodendrid stems was

provided primarily by an inordinately thick zone of modi

fied periderm (Walton* 1 9 5 3 ). The plants produced rela tively small amounts of secondary xylem. On the basis of the radial arrangement of conducting cells, and the occur rence of a well-developed ray system* it was suggested rel atively early in the study of anatomically preserved Car boniferous plants that the wood of arborescent lycopods was

produced by a vascular cambium (Williamson* 1872a*b). Fur thermore* it was recognized by some (e-g.* Williamson*

1872b; Seward and Hill* 1900; Seward* 1902) that the gener ative layer responsible for producing the wood, while simi lar in many respects to that of modern seed plants* was functionally unifacial and only produced cells centripetal ly- Other early workers (e.g., Weiss* 1901; S c o tt* 1920)* ill contrast* suggested that a small amount of secondary phloem Mas produced* but that* because of the fragile

nature of the tissue* it was rarely preserved. More recently* this topic has become the focus of further inves

tigation. Based on the examination of cross sections fro® several sell-preserved diminutive lepidodendrid axes*

Arnold (1960| concluded that Mif there was a cambium (in

the arborescent lycopods)«..it produced secondary xylea only-61 In contrast,* Lemoigne (1962) observed that the

position and arrangement of certain thin-wailed cells in the extraxylary zone of several lepidodendrid stems bere

suggestive of secondary phloem. Later* however* he with

drew the aspect of certainty from his initial statement

(Lemoigne* 1 9 6 4 )* and ultimately he concluded th a t the t i s sue in question was probably not conductive* and thus* that extensive amounts of secondary phloem were apparently not produced in the lepidcdendrids (Lemoigne* 1 9 6 6 ). The most recent study on this subject (Eggert and Kanemoto* 1977)

provided additional documentation for the presence of a unifacial cambium in the arborescent lycopods and* on the basis of a comprehensive analysis of the tissues in the three major planes of section* clarified the developmental nature of the extraxylary tissues. I t was shown that the radially aligned thin-walled cells that had freguently been

mistaken for secondary phloem were actually derived from a phellogen-like meristem that developed within an extrasy-

lacy pare nch yma to us sheath® Eggert and Kanemoto suggested

that the phloem was exclusively primary in development and

localized in discrete strands at the periphery of the par

enchymatous sheath® Similar conclusions sere made in the

study of Chaloaeria* as unusual Dpper Pennsylvanian cor-

lose lycophyte with secondary growth fPigg and Bothwell g

1983} ®

In addition to the cambium in the lepidodendrids being

unifacial, it was also apparently a determinate meristem.

Based on the analysis of several specimens of Leridophlo-

ios Andress and Murdy (1957) regarded the pattern and

arrangement of primary xylem as suggestive of the following

ontogenetic scheme for stem growth: (1) A large shoot api

cal meristem formed early in the development of the stem

and remained undiminished in size for an extend period of

time forming a tall unbranched trunks (2) the shoot apex

ultimately underwent a series of dichotomies producing

branches that became progressively smaller with each divi

sion® A more comprehensive investigation (Eggert0 19 61)

involving a large number of specimens confirmed earlier

speculation and provided additional details on the charac

teristics of stem growth in the lepidodendrids® It was shown that primary development in these plants conformed to

a seguence of epidogenesis, menetogenesis, and apoxogeaesis 10

culminating in the production of a determinate apical user”

istem. Based on the preliminary conclusions of Andrews and

Hurdy (1957), Arnold (1960) proposed that the vascular cam

bium, like the apical meristem, might also have functioned

for a limited interval and, thus, that the unusual appear

ance of the extraxylary tissues in the fossils might be

explained by the relative maturity of the stem at the tiie

it «as preserved*. (In general, definitive cambial initials

have never been recognized, even in stems which exhibit

complete cellular preservation-) A mold 9 s suggestion was

later confirmed by Eggert and Kanemoto (1977) in an analy sis of Lepidodendron phloem, where it was shown that the

distinctive organization of extraxylary tissues resulted from the dedifferentiation of the cambium. The arrangement

of the tissues is apparently similar to that observed in certain woody dicots that exhibit determinate growth (e.g.,

Hilton, 1938; Eames and HacEaniels, 1947).

Belatively early in the study of Carboniferous plants, it was established that Stigmaria was the underground axis of lepidodendron and Siqillaria (Binney, 1846)® Thus, an historical account of the various interpretations of secon dary structure in stigmaria fellows closely that of lepi dodendrid stems. In 1887, Silliamson demonstrated that the wood of Stigmaria was formed by the activity of a vascular cambium. He illustrated a zone of extraxylary tissue com- 11 posed of elongate parenchymatous elements with horizontal

endaalls which he inters ret ted as "cambifcrm products 89 derived from a secondary meristematic layer® lilliaason. was noncommittal as to whether or not the cambium was bifa cial and elected rather to note that analysis of his speci men could not not provide a definitive answer to this ques tion® Somewhat later* , i e i s s {19011 assumed an am biguous stance on this problem* describing a zone of "primary” phloem tissue outside of the Gambia1 cylinder® la some cases the cells of this zone were observed to be arranged

in "fairly regular radial rows - ' 8 In contrast® Scott (19 20) indicated that secondary phloem was present in ’’more cr less radially arranged" files external to the remains of the cambium. The nature of secondary growth in Stigmaria was not addressed further until Frankenturg and Eggert*s comprehensive investigation in 1969® Based on the analysis of several well—preserved specimens* it was suggested that the vascular cambium was unifacial® Similarly* in associa tion with the general pattern of primary development in the lepidodendrids (Eggert* 1961) it was suggested that the cambium in these axes was determinate® In some of the material* a narrow band of tissue composed of uniform* small-dia me ter tracheids was observed around the periphery of the secondary xylem. It was suggested that this tissue was produced by the determinate vascular cambium during the 12 final stages of growth and was classified as "terminal

Hood," Other developmental phenomena related to secondary growth include the apparent increase In size of the large rays associated with the lateral appendage traces (Hilliam- son* 1889s Frankenfcurg and Eggert* 1969) and the "stabili sation” of cambial activity early in the development of the soo(L Hith respect to the latter* it was observed that the width of the first several secondary tracheids was variable and that the diameter of later-formed cells was relatively constant* suggesting that the size of the fusiform initials became stabilized during development*, Likewise* if was suggested that the tracheids of the first-formed secondary xylem were longer than the outermost metaxylem elements as in modern seed plants (Bailey* 194h)- Finally* on the b a s is o f the tiered arrangement of the tracheids within a radial file* it was suggested that a uniform amount of cell elongation occurred during the maturation of cambial deriv atives in Stigmaria.,

SFaBMOFflg l lM.ES

In contrast to the lepidodendrids* which were apparently all arborescent * members of the Sphenophyllales are gener ally depicted as low-growing* understory plants (Taylor*

1981)*. Sphenoph v llu m » th e most common C a rb o n ife ro u s re p resentative of this group* is usually reconstructed as a prostrate or scrambling woody vine (Bafcenturg* 1982)-

Although the majority of stems tend to he no larger than

10-12 a® in diameter (Baxter* 1948; Eggert and Gaunt*

1973)* larger axes with diameters in excess of 20s® are occasionally discovered (Darrah* 1968; tfa* 1977)- The sec ondary xylem in Sphenophvllua is composed of alternating

wedges of fascicular and interfascicular 2 wood t h a t r a d i a t e from the triarch protostele. In the interfascicular regions* the diameter of the tracheids remains relatively constant from the inside to the outside of the wood® In contrast* in the fascicular zones the diameters of the first-formed tracheids are relatively small® In the course of secondary development* however* the cells gradually increase in size so that near the periphery the elements in both zones are identical in appearance. Aside from tracheid diameter* the two zones can also be distinguished on the basis of the parenchymatous aspect of the wood. In the fascicular areas* discontinuous radially and tangentially disposed strands of parenchyma are present in addition to multiseriate rays. The latter are often continuous across

2 When dealing with Sphenophvlluma the terms 81 fascicular 88 and '"interfascicular 91 are used in the manner first desig nated by Hilliamson and Scott (1894). Fascicular refers to secondary xylem produced opposite the protoxylem points. Interfascicular indicates the wood formed oppo site the sides of the protostele between the protoxylem groups. This usage differs from the normal (sensu Esau* 1965) in which the former refers to tissue associated with individual cauline vascular bundles or sympodia and not merely protoxylem- 14

the entire radial thickness of the secondary xylem- The innermost interfascicular wood apparently lacks true rays and is characterized by zones of radial and tangential par enchyma (Hilliamson and Scott, 1894; Eggerfc and Gaunt,

1 9 7 3 ).

It Has suggested before the turn of the century that the wood of Sphenophvllum aas secondary in origin, and pro

duced by the activity of a vascular cambium (Renault, 1873;

Williamson, 1874; Van liegham, 1889)• Renault (1873, 1882,

1885), filliamson (1874), and Williamson and Scott (1898) were apparently the first to investigate the developmental character of the meristem- The latter workers presented evidence which suggested that secondary phloem was produced in insigne and, thus, that the lateral meristem was functionally bifacial. Williamson and Scott (1898) also

described a tissue in S. plurifoliatum that was inter

pret ted as secondary phloem. 1 more recent study of this taxon, however, showed that the illustrated cells were not those of the phloem (Eggert and Gaunt, 1973). Rather it

was suggested that the distinctive extraxylary zone was the product of a deeply seated cork cambium. Subseguent analy sis of other specimens indicated the presence of secondary phloem thus providing evidence that the cambium in this

species was indeed bifacial as suggested by earlier work e r s . Eggerfc and Gaunt {1973) suggested that a determinate

p a t t e r n of growth might also have been present in Spheno-

phyilum. In contrast to earlier mock dealing with calamites and lepidodendrids (Eggerfc, 1961, 1962), however, the pro posal that growth in Sphenopfavllum was determinate was

based on the apparent acropefcal reduction in leaf size and complexity. Assuming that apical development was short

liv e d g it was proposed that the moderately thick zone of

parenchyma cells located between the last—formed secondary

xylem and the phloem was produced by the dedifferentiaticn of the individual cambial initials. Previous workers (Wil

liamson and Scott, 1898; Darrah, 1968) had concluded that the tissue represented the actual cambial cells. Eggerfc

and G aunt { 1973) term ed th e zone "a p o s t—me r is te m a ti c 91 • p a r enchyma sheath to distinguish it from the primary parenchy ma sheath that surrounds the primary xylem in numerous p terid ophy tes.

Additional statements have been made regarding cambial development in Sphenophyllurn as deduced from the examina tion of secondary xylem. Based on the appearance of the wood in cross section, Schabilion (1969) proposed that cir cumferential enlargement of the cambium resulted from { 1 ) anticlinal division of cambial initials, indicated by an increase in the number of radial files of xylem cells, and

( 2 ) an increase in the tangential dia me ter of cambial 16 cells, reflected in the increase in size of the tracheids®

Along similar lines, a preliminary investigation of inter

fascicular wood development revealed that there was a dra matic iacrease in tracheid length from the inside to the outside of the wood (Cichan and Taylor, 1982)® Assuming

that this change reflected a gradual increase in the size of the fusiform initials, it was suggested that this phe nomenon might have been involved is increasing the circum f e r e n c e o f t h e cambium®

E01I1SETAS.ES

An arborescent component quantitatively less significant than the lepidodendrids (Phillips, 1980^ Phillips and DiMi chele, 1981), but no less distinctive from a structural viewpoint, were the woody members of the Egoisetales®

Although plants in this group are primarily thought of as

t r e e s and s h r u b s , a t t a i n i n g maximum h e ig h ts of betw een 2 0 and 30 m (Grand •Eury in Scott, 1920) more diminuative vine-like members are also hnoan to have occurred (Cichan and Taylor, 19 83) . In contrast to the lepidodendrids, cauline mechanical tissue was primarily in the form of secon dary xylem, and little (Cichan and Taylor, 1983) or no per iderm (Agashe, 196 4) was produced® Three genera of anatomically preserved calamite stems are presently recog nized (Andrews, 1952) on the basis of the organization of 17 the secondary xylem. Hood in this group is composed of alternating fascicular and interfascicular segments. The former zones are composed of lignified elements (tracheids) and parenchymatous rays. The interfascicular component, also called principal (Scott, 1920? Good, 19751 or primary

rays (Andreas, 1952 1 Anderson, 195*4) , are composed of par enchyma or specific combinations of parenchyma and scler- enchy ma depending on the g e n u s. By f a r th e m ost common genus in Euramerican coal balls (Andreas, 1961), and the one which has been examined most extensively, is Arthropi- tvs. The wood in stems of this type is characterized by broad, wholly parenchymatous interfascicular rays that radially either decrease in size (e.g.® A. communis —

Binney, 1868) , maintain approximately the same tangential dimension (e.g., A., versifoveata - Andrews, 1952) , or become dilated (e.g., iU deltcides - Cichan and Taylor,

1983). The abundance of secondary xylem in these stems clearly points to the fact that a vascular cambium was present (Andrews and Agashe, 1963) , but, as in the lepidodendrids, there is seme dispute over the actual structure and activity of this meristem.

Because of the delicate nature of phloem tissue, it is rarely preserved in aerial calamitean axes (HiIson and

Eggert® 197*4). I n stem s in which phloem h as been r e p o r te d

(Renault, 1893, 1896; Agashe, 196*4? Cichan and Taylor® 1983)® the general position and appearance of the tissue

suggests that it is primary in origin® for reasons that

are not entirely clear® the phloem in calaaifceaa roots

(i.e.® Astrofflvelon) is apparently more frequently pre

served than that in stems (Hilson and Eggert* 1974)® la

these axes® both primary and secondary phloem have teen

described® the latter being found most frequently in the

largest and presumably oldest specimens (Agashe® 1964s lilson and Eggerfc® 1974)® General histological features of

the secondary phloem® however® do not conform to those of

similar tissues in modern arborescent plants (Agashe®

1964) ; the quantities produced are extremely limited® the

radial alignment of the cells is not pronounced® and the

elements are generally rather short- Moreover® sieve areas

have not been demonstrated in the elements interpretted as sieve cells- Thus® on the basis of the descriptions pro

vided in the literature® two alternate hypotheses are pos sible regarding the nature of cambial activity in the calamites; (1) In the stems® the vascular cambium is uni

facial® and in the roots it is unifacial early in develop

ment and gradually becomes bifacial- (2) She cambium in

both the stem and the root is unifacial® and true secondary phloem is not produced in the underground organs.

like the arborescent lycopods® primary development in th e c a la m ite s a p p e a rs to have been d e te r m in a te (Eggerfc® 1962) . Evidence has been presented to Indicate that shoot ontogeny was characterized by a sequence of epidogenetic, menetogenetic, and apoxogenetic growth, followed by the permanent inactivation of the apical meristem* la vies of the fact that lateral development by a vascular cambium is directly controlled by the activity of the shoot apex

(Brown, 1S71 s P h i l i p s c n e t a l , 1971; B o b e r is , 1976) g i t i s not surprising that histological evidence has been present-* ed for a determinate cambium in the calamites. Generally speaking, definitive cambial initials have yet to be observed in the group, even in axes characterized by well- preserved extraxylary tissues. Ihis has been interpretted as demonstrating not only the extremely delicate nature c£ the Initials, but also the determinate character of the meristem (Eggert, 1962). nore direct evidence of determi nate cambial growth has been reported in well-preserved

Astromyelcn axes, where elements of the last-formed secon dary xylem were observed to abut directly on the more peripheral parenchymatous tissue (iilson and Eggert, 1974)»

On the basis of the close juxtaposition of these tissues, it has been suggested that the initials of the vascular cambium must have matured into secondary tracheids during the terminal phases of meristematic activity.

Another developmental phenomenon involving the vascular cambium that has been examined only marginally in this 20

group, are changes in the composition of the aeristea.

Inferfascicular raj closure was that process is calamites

whereby the interfascicular raj segment decreased in tan

gential width during the course of secondary development,

fielatively early in the study of the calamiies it was sug

gested that the process occurred by the conversion of ray

initials to fusiform initials fiilliaason and Scott, 1894s

Scott, 1920)o hi H i am son and Scoff (1894) noted that, when

the interfascicular rays of Arthronitvs communis were

observed in radial section, the rows of parenchyma were

'"’gradually succeeded by (rows of) tracheids ® 88 It was also

observed that the "tracheids make their appearance at vari

ous places in the interior of the ray.. . and that the inter

fascicular tracheids probably arose by the elongation of

cambial cells . 88 Similarly, Scott (1920) concluded that

"because the tracheae are very long, and the cells they

replace are very short, and yet the radial arrangement of

the elements is not disturbed , 88 the change "must have taken

place In the cambial cells . 88 1 parallel phenomenon has

been reported in jU deltoides. a stem characterized by

Interfascicular rays that broadened as the stem girth increased (Cichan and Taylor, 1983). In these axes, an

increase in ray cell width accompanied ray dilitation, and

if has been suggested that the tangential enlargement of

individual ray initials was responsible for widening the 21 ray. On the basis of this information? as sell as data on the enlargement of secondary ray cells? it was proposed that increasing ray initial size played an important role in circumferential enlargement of the cambium in this plant*,

BBDOULQSik&BS

The medollosan pteridosperms? second in overall abundance only to the arborescent lycopods in the Upper Pennsylvanian coal swamps (Phillips? 1980)? represent one of the most distinctive groups of seed plants. Stems included in this group are characterized by one to many zones of primary vascular tissue? and each segment is surrounded by an irregular cylinder of secondary xylem. In early works on medullosan stems? each vascular segment was regarded as a stele? and therefore the axes were classified as polystel- ic. Recent analysis (Basinger? Bothwell? and Stewart?

1974)? however? suggests that each "stele” actually repre sented a portion of a large? highly disec ted eustele? and thus the primary vasculature conforms closely to the pat tern found in other gymaosperms (Namboodiri and Beck?

1968a?b?c). At present? only tso of the four major stem genera included in the Medullosaceae are known to have existed in the Pennsylvanian? Medullosa and Sutcliffia.

The former is also well known from the Permian? and both 22 genera have representatives in the Loner Carboniferous

{Scott* 1899* 1906)- 7he strafigra phic distribution o f th e o th e r two medullosan stems* Quaestora (Mapes and Rothwell*

1980) and Colnorvlon (Renault* 1893* 1896)* is apparently more r e s t r i c t e d ; the former occurs only in Mlssissippian sediments* and the latter Is known only from th e Permian*

Sutcliffia and Hedullosa can be distinguished from one another by the distribution of cauliae vascular tissues*

In Sutcliffia there are generally one or two large vascu la r strands surrounded by numerous smaller bundles* Form ing a sheath around each individual segment is a relatively small zone of secondary vascular tissue* In Hed u llo s a * on the other hand* there is no discernable pattern in vascular strand size* and the number of segments ranges from two to th ree i n n o e i (Steidtmann* 1944) to approximately 23 in M«. primaeva {Stewart and Eelevoryas* 1952) * In con t r a s t to Sutcliffia. relatively large amounts of secondary vascular tissue were apparently produced by all species of

H e d u llo sa .

The distinctive anatomy of medullosan stems has prompted considerable discussion about the growth habit of the plants* Several different configurations of cauliae mechanical tissue are known in the group* and a wide degree o f variation occurs in the pattern of secondary xylem pro d u c tio n . Important characters in this respect are the 23 amount of wood formed and Its symmetry about the vascular segment, namely, endocentric (i-e., disproportionately large amounts formed ceniripetally), egocentric (i.e., dis proportionately large amounts produced centrifugally), and normal (i.e., equal amounts formed centrifugally and cen tripetal!y) patterns have been described, and each has been designated as having different mechanical/structural prop erties (Schopf, 1939). On the basis of Schopf Ss work, Eas

ter (194 9) suggested that the group aas characterized

almost exclusively by scrambling vine-like forms with rela tively few, if any, arborescent types. An analysis of pre

viously described taxa and more recently discovered speci mens, with special emphasis directed at recognizing ontogenetic variability, prompted Eelevoryas (1955) to place many of the species in synonomy. Differences in the distribution and arrangement of vascular tissue were gener ally attributed to the different developmental ages of the specimens. Delevoryas showed that there was little evi dence to indicate a scandeni habit of growth and concluded that the plants exhibited a self-supporting upright form of growth with maximum heights in excess of 2s. Hore recent ly, Stewart (1983) proposed that the maximum heights attained by medullosans were in the 3.5 to 4.5 a range.

The stems of Hedullosa are unegualled in the Paleozoic with respect to the range and diversity of secondary growth 24 phenomena that hawe been observed. Not only were a well- developed phellogen and vascular cambium present, but numerous localized accessory meristems are also known to have occurred, especially in the older# larger portions of certain plants., Tissues produced by the anomalous aeriste- matic zones range from parenchyma to bundles of tracheid- lilce cells produced ia “star rings8® (deFraine* 1914) .

Based on the detailed analysis of cauliae tissues in sever al specimens# Delevoryas (1955) proposed that the tradi tional distinction between primary and secondary growth did not exist ia Hedullosa. at least as far as vascular tissue production was concerned. To explain the consistent corre lation between the size of the vascular segment and the amount of wood produced, it was suggested that the vascular segment continued to increase in size throughout the entire lifetime of the plant. This process is thought to have been the result of diffuse meristemaiic activity of persis tant procambial cells within the strand. The tissues that were apparently formed included both ground parenchyma and bundles of conducting elements. It is envisioned that vas cular segment enlargement and wood accretion were simulta neous events and that disruption of the rigid lignified tissue was prevented by progressive cellular readjustments in the parenchymatous secondary rays. Possible evidence for the latter phenomenon is found in large specimens. 25 ahere wood rays closest to the “primary 89 strand sere

Disserted to be broader than those at greater radii (Schopf*

19395 S teidtm ann* 1944; S tew art* 1951}® A s o r e r e c e n t study of the arrangement of the vascular segments in

Hedullosa,* however* suggested that the unusual relationship between the primary and secondary conducting tissues could be attributed more reasonably to the activity of a determi nate apical meristem (Basinger* Eothwell* and Stewart*

1974}« In this respect* primary development may conform to a® apoxogenetic pattern of growth® Ihile it is clear that both hypotheses have some merit* neither of them have keen uneguivocably proven* and at present each remains a viable alternative (Stewart* 1983).

Despite the distinctive process of primary stem develop ment in Hedullosa* the vascular cambium appears to have been normal in structure and activity® Both secondary xylem and phloem were characterized by a sell-developed axial system of conducting elements and parenchymatous hor izontal rays® The radial continuity of cell files fro® xylem to phloem is evidence of the bifacial nature of the cambium (Scott* 1899; deFraine* 1914^ Baxter* 1949; Smoot*

1984)® As noted earlier* the pattern of secondary tissue distribution about the vascular segment is usually asymme trical and smaller quantities of tissue are generally pro duced along the lateral margins of the segment® In this 26 regard* it has been suggested that cambial activity was probably not initiated simultaneously around the vascular segment* the meristem differentiating later ia the lateral zones (Delevoryas* 1955)- A number of workers have described features of wood structure that suggest the pres ence of a determinate vascular cambium in Medullosa,, although absolute statements in this respect require proof of limited apical growth*, In eu noei„ for example*

Schopf (1939) and Stewart (19 51) observed a gradual reduc tion in tracheid diameter in files produced toward the periphery of the wood similar to the "terminal wood" of certain lepidodendrids (7tankenberg and Eggert* 1969).

CORDAJTALFS

Anatomically preserved plant parts attributable to theCor- daitopsida occur with relatively high frequency in coal balls of the Upper Carboniferous (Phillips* 1980)„ Stems of this group are easily recognized by their unusually large septate pith and characteristic pycnozylic wood*,

Presumably on the basis of their distinctive appearance* and the important role the cordaites may have played in the

evolution of modern conifers (Florin* 1951; Beck* 19 6 6 *

1981)* the stems have been the subject of numerous studies since their affinities were first recognized in the late

1800®s- Except for the broad pith traversed by closely 27 spaced septa* the stems bear a striking resemblance to those of modern conifers,, Because of this close anatomical similarity* the classic whole-plant reconstruction by

Grand *Eury (1877) depicts the average individual as arborescent in form* aith heights in excess of 2 0 a

(Grand®Eury in Scott* 1920) . & more recent interpretation* however* based on the apparent aerial nature of the roots* suggests that the cardaites were such smaller plants* with a general habit similar to that that of modern mangroves

( C rid la n d , 1964) .

The taxonomic history of anatomically preserved cordai- fean stems is complex* in part resulting from inconsistent tissue preservation, fragmentation of the axes, and the unknown factor of ontogenetic variability. Features that have traditionally been used to distinguish taxa at the generic level are almost exclusively those of the primary body, especially the morphology of the xylem bundles and leaf traces (Renault* 1896; Scott* 1902; Maslin, 1911).

Because of the simple, rather homogeneous appearance of the secondary xylem within the cordaites, this tissue has been of relatively little value in distinguishing taxa. Thus, when found as isolated fragments, pieces of wood cannot be assigned to a particular cordaite genus (Wilson and John ston, 1940), but, rather, must be designated as Dadoxvloa

(Vogellehner, 1964). Over the years, this genus has come 28 to represent a repository for pycnoxylic Paleozoic wood with uniseriate or biseriate rays ranging fro® one to thir ty cells high* The most distinguishing character of

Dadoxvlon^ however® is the nature c£ the tracheids® which are usually about 35 urn broad and exhibit circular bordered pits arranged in a uniseriate or biseriafe pattern on the radial walls. Hood with the saie general structure Is also known from the Mesozoic and has been classified as Iran- carioxvlon based on its resemblance to the wood of extant

Araucariaceae (Knoulton® 1890® although see Jeffrey® 191%)=

Because the tissue was produced in relatively large amounts and is modern in appearance® most workers seem to have assumed that cordaitean wood was formed as it is in living c o n i f e r s .

On the basis of the discovery of numerous well-preserved specimens® especially those from Eritian and Europe® it was suggested early in the study of cordaitean stems that a vascular cambium was present (Maslen® 1911). Mot only did the meristem produce abundant weed® but relatively large amounts of phloem were also formed (Renault® 1896; Maslen®

1911® 193 0; Scott® 1912® 1918; Cohen and Delevoryas® 1959).

There can be little doubt thaf the phloem was secondary in development since it is composed of well-ordered files of cells that are radially continuous with those of the wood

(Maslen® 1930). Thus® the cambium was apparently bifacial. 29 little else has been written about the vascular cambium or wood development in cordaites* and the majority of recent work deals mainly with taxonomic problems in the group.

As the preceding discussion indicates* the level of understanding of secondary vascular tissue production in

Carboniferous plants is deficient in a variety of areas, ihile general histological features have been examined to some extent* important questions dealing with developmental processes have yet to be comprehensively addressed. In this respect it is* at present* unclear whether or not cir cumferential enlargement of the cambium was accommodated by anticlinal division of the fusiform initials. Furthermore* if anticlinal division of the initials was associated with cambial expansion in these primitive plants* was the pro cess similar or different to that observed in modern groups? On the otherhand* if evidence for such divisions is lacking* then by what mechanism was enlargement of the meristem accommodated? Thus* the purpose of the present study is to investigate the structural and developmental aspects of secondary vascular tissue production in several of the more important Pennsylvanian plant groups. Primary emphasis will be directed toward characterizing the phenom enon of circumferential cambial enlargement and the devel opmental changes that occurred in the cellular composition of the cambium. Chapter II

SA1E1IALS M S BEXBODS

1 1 1 of the specimens used in this study are anatomically preserved axes found in coal balls from the Pennsylvanian o£ North America. The following is a listing of the speci mens examined. Unless otheraise indicated^, coal ball des ignation numbers refer to the CSU collection. Infcreation regarding the location of collecting sites is included at the end of this listing.

SPECIHEN DIRECTORY

Coal Ball No. Locality Saxon

Le pid ode nd r a le s :

99 SB Paralycopodites brevif alius 104 LC St I t 31 99 129 LC I t 19 m 99 225 SB Lepidodendron dicentricuE 244 sa Lepidodendron sc le ro ti c urn 551 SA SS G3 98 99 1536 LC Paralycopodites hrevifalius 1712 LC II 99 99 98 7294 LC @9 §9 SB 99 8899 LC m 91 98 99 822 SA Stiqmaria ficoides 2098 LC 99 91 99 m 6526 LC 98 99 39 99 6699 LC m n S3 J 8 8 8521 LC n 99 91 91 8749 LC n 93 S3 33

- 30 - 31

Sphenophy H ales:

60 SB Sphenophyllurn pluxifoliat 105 LC SI £ i n 159 PB 01 33 w t i 186 LC 91 n 81 n 209 LC 91 93 i t 81 220 LC B! 89 St 81 98 53 227 PB 93 33 254 SA m 31 99 H 662 SB S3 SI ft 88 SI 99 H 88 689 SA 1028 1C a w IB 88 1 033 SE m S t 91 88 1989 SA « 68 31 91 21 06 LC 31 39 91 81 2142 LC at 93 a s i n 31 39 M 2539 SA 2615 SA n n (1 H 5930 PF m «s 11 88 6620 LC m 91 a n 6649 LC 33 f t n 7143 LC 31 St 11 81 72 82 LC •1 89 M W 8525 LC S3 St U It

E guisetales:

2017 LC A rthropitys communis 6542 LC II 98 88 IB 6627 LC 91 n 98 IB 6643 LC 89 98 91 81 6672 LC 91 99 08 99 6684 LC 98 99 88 S3 7037 LC 89 98 88 99 7051 LC 98 98 99 91 8539 LC m £3 S3 90 8576 LC m 98 91 n 8591 LC si 98 99 89 9506 LC 88 99 98 84 95 07 LC 81 BC SB 88 9515 LC 89 88 Si n 9518 LC n SI 81 89 95 LC A rth r o p i tv s d e l t o i d e s 209 LC n 18 n _JI 1808 LC 99 99 91 81 7290 LC 83 98 II 91 32

Kedullosales:

365 BV M edullosa n o ei 371 BV 81 IS §8 678 BV W 88 89 831 BV m la m 861 BV n IS n 1239 BV n 81 m

C o r d a i tales:

33 WJO i m * Cordaixylco sp. 63 1X0 Hfl S3 a 930 OK UE m m m 1014 UK m E esoxyIon spa 1190 ESO m e Cordaixylon sp. 1500 UK MB n u n 2130 ESU SC n a a 4507 ESU AC nan

ESU = Paleobotanical Collection, Department of .Biology,

Emporia State University, Emporia, KS

OSU = P-aleobotanical Collection, Department of Botany,

The Ohio State University, Columbus, OH

UK = Paleobotanical Collection, Department of Botany,

University of Kansas, Lawrence, KS

W1U = Paleobotanical Collection, Department of Biology,

Sestern Illinois University, Kacomfc, IL.

L o c a l i t i e s

B¥ = Berryville, II; Upper Pennsylvanian, Calhoun Coal,

Mattoon Formation, Mcleansboro Group, Sumner 15®

Quad. {Sec. 7, T2N, E13H), Lawrence Co., 1L.

LC = Lewis Creek, KY; Lower-Middle Pennsylvanian, =Hamlin

Coal, Breathitt Formation, Cutchin 7.5 * Quad.

L e s l i e C o - , KY. 33

MC = Mackie-Clemens No® 23 Mine, Biddle Pennsylvanian,

Be vier Formation, Cherokee Group, Joplin Quad®

(Sec® 2 1 , *E9S, £ 2 5 E) , C ra n fo rd Co. , KS®

MC = Hew Calhoun* IL; Upper Pennsylvanian, Calhoun Coal®

Mattoon Formation* Meleanshore Group* Sumner 15®

Quad® (Sec® 32* 1 3 N* E 14 W)* H ich lan d Co.* IL®

PS = Providence* KY; Middle Pennsylvanian* Mo® 11* 12*

or 13 Kentucky Coal* Baker Coal Member* Lisaan

Formation® Allegheny Series* Providence 7®5 9

Quad® (37 2 4 952 1/2"N , 87 46® 9"W) * W ebster

Co®* KY®

SI = Sahara* II; Middle Pennsylvanian* Herrin (No® 6 )

Coal* Carbondale Formation* Kewanee Group*

Harrisburg 15 * Quad. (Sec® 30, T9S R4E),

W illiam so n Co®, XL®

WM = West Mineral, Kansas; Middle Pennsylvanian, Fleming

and/or Mineral Coals, Cabaniss Formation, Cherokee

Group, Des Moines Series, Columbus 15® Quad® (1 1/2

Sec® 5, I 33S, R 22 E). Cherokee Co-, KS.

fBCBIJQOES

Most of what Is presently known about camiial development

living plants has been obtained through the analysis of derivative vascular tissues. Because the initials divide

repeatedly in a periclinal fashion, they leave a record of 34 their appearance in the files of xylea and phloem cells.

Information about progressive changes in cell size, the multiplicative formation of nes initials, and variations in the amounts of ray and fusiform initials can be g le an e d from analyses of serial tangential sections of secondary vascular tissues. Whereas early workers (e.g., Klinken,

1914) utilized the secondary phloem in studies of cambial development, more recent investigations (e.g., Evert, 1961;

Cumbie, 1963, 1969 a, b; Bannan, 1964 and references of

Bannan cited therein) have focused almost exclusively on

secondary xylera because the cells of this tissue are ( 1 )

less likely to subdivide during differentiation, ( 2 ) more resistant to distortion and abcission, and (3) produced in greater quantities than the phloem cells. For these rea sons, analysis of xylem has the potential to yield a more accurate picture of the cambium than study of the phloem

(Bannan, 1950; Pliiiipson et al, 1971).

In the present investigation, radial files of Mood cells were examined in transverse and serial tangential sections t h a t Mere prepared using the cellulose acetate peel techni que (Joy, Willis, and Lacey, 1956). Tangential prepara tions were obtained at radii measured in intervals of 0.5mm or less. In specimens that passed obliquely through the coal ball slab, the actual radius (Sa) was determined from the measured radius (Sm) using the following formula:

Sa = Sm x cos8 35

where 3 = the angle of the axis in the coal ball

si ah (fig- 1 } -

From each tangential wood section a the following 3ata were

o b ta in e d ; (1) P e r c e n t tr a c h e i d a re a (2) P e r c e n t r a y a re a

(3) Tracheid length (4) Tracheid width (5) Bay cell length

( 6 ) Bay cell width.

Percent tracheid and ray areas aere determined using the

Zeiss lideoplan Image Analyzer and Combined Programs ver

sion 5-22- Two representative rectangular areas of wood

each approximately 2-0 x 3.0 mm, were selected at random

and traced on a digitizing pad using a Zeiss camera lucida

drawing tube. The measured area was designated as the

total wood area (A). Each ray within the rectangular area

was then traced and the individual areassummed, thus

yieldingthe measured ray area (Ap). Tracheid area (At)

was calculated by subtracting Ap from A, and percent areas

for the two components were determined as follows;

T = At/A & 100

P = Ap/A x 100 (2)

In Arthropitys communis and the cordaites, tracheid length (Lt) was measured directly from tangential sections using an ocular micrometer. Mean values were determined on the basis of a minimum of fifteen counts. Poor preservation usually precluded attempts to obtain large sample sizes |i.e.® where n>50) * which may have provided more accurate estimates of mean cell length. In Paralvcopo- difces. Stigmaria „ 6 . deltoides. Sphenop hvllub. and

Hedullosa. tracheid lengths generally exceeded the thick ness of the coal ball slab* and* thus* only parts of tracheids were represented in individual sections. Since direct measurement in such cases was impossible* alternate techniques were employed to obtain estimates of cell le n g t h .

In Sphenophvllum. tracheid length was determined using cell reconstructions based on serial transverse sections obtained at measured intervals (Cichan and Taylor* 1982).

Although the technique was found to provide accurate esti mates* it proved to be extremely time consuming and tedi ous. Thus* alternate methods were employed in the study of the other t axa. In the lepidodendrids* Arthropitvs del- toidesa and Medullosa* tracheid lengths were estimated using a variation of the technique described by Cichan and

Taylor (1984)» In this variation* longitudinal wood sec tions were utilized instead of cross sections to arrive at potentially more accurate approximations of cell length.

Cell length was determined for the innermost wood sections only* i.e .* the sections made for each specimen at the smallest radius. This value was designated as the initial 37 tracheid .length (L ti) . In the mote peripheral sections, i.e., these obtained at progressively larger radii, tra cheid length values (It) Here represented as the sun cf the initial tracheid length and the mean net change in tracheid

length (delta It) e i . e . ,

Lt = Lti * delta It

The latter parameter was determined by locating and follow ing the individual tracheid tips in files from the inner to the outer wood. in each section, the axial distances between the tips and a fixed reference point in the wood were measured and mean values calculated. An equal number of " upward*' and "down ward11 pointing tip s were examined, and means were determined based on the analysis of a minimum of twenty tips. lip position in the innermost sections was set to equal zero, and subseguent measurements were adjust ed accordingly- Ih us, tracheid length estimates were all ultimately related to those of the innermost sections- Iracheid width (St) and ray cell height £Lp) and width

PP) were measured using the Zeiss Videoplan Computer Sys tem. Tracheid width is here defined as the tangential diameter cf the widest portion of the cell where opposite walls of the tracheid are parallel- Bean values of this parameter were calculated on the basis of a minimum sample size of fifty cells- Ray cell length and width are here 38

d efin ed a s th e w id est and longest axes of the cell* respec

tively,. Hean values of these parameters • were determined

u sin g a minimum of one hundred cell counts* Data were ana lyzed and graphics obtained using the SAS statistics pro

gram s (SAS Institute Inc* „ Raleigh* North C a ro lin a ) main

ta in e d on the Ohio State University XRCC Amdahl 470 com puter*

Bhereas previous studies of cambial development in

e x ta n t plants have focused primarily on qualitative f e a 

tures* the present investigation emphasizes loth qualita

tive and quantitative aspects of secondary xylem produc

tion* In this respect* a two-dimensional mathematical

model describing cambial growth was designed in order to

provide data on changes that take place in the number of initials as the cambium is displaced radially. The model

differs from others that have been proposed to study cambi-

a l developm ent (H ilson* 1964; fiilscn and Howard* 1968) in

that it focuses on multiplicative cell divisions rather

than additive divisions. She cambium is envisioned as a c y lin d e r (Fig* 2) with an area (Ac) defined as fellows:

(3)

Ac = 2 i 7T x S x H where S = radius and

H = cylinder height (in this and all subsequent equa

tions* H is arbitrarily set equal to unity). 39

The a r e a o£ t h e cam bial cylinder can also he expressed as th e sum o f hofh the area of the raj initials (hr) and th e fusiform initials (Af)» Thus*

{•*)

Ac ~ Af ♦ Ar

The total fusiform initial area and total raj initial area c a a also be expressed in two ways, as a function of the total cambial area and as a function of cell size* Thus*

(5)

A£ = F x Ac

( 6)

Ar = B x Ac

where F = p e r c e n t composition of fusiform i n i t i a l s * and

B = percent composition of ray initials.

(7)

Af = I f x H£ x N£

( 8 )

Ar = Lr x ¥r x Mr

where If = fusiform initial length

If = fusiform initial width

Mf = number of fusiform initials

Lr = length of ray initials

hr = width of ray initials

Nr = number of ray initials 40

Combining Egnation No. 3, E q u atio n No. 5 , and Equation No.

7g a s s e l l as E q u atio n No. 6 and Equation No. 8 and s o i l in g for Nf and Nr yields

19)

F x Ac

L£ x W£ and

C10)

H x Ac Nr = —------l r x Hr

Thus® u s in g E q u a tio n No. 9 and E q u atio n No. 10, i t i s p os s i b l e to calculate the number of fusiform initials and ray initials in the cambium at any designated radius. Because the shape of the tr a c h e id s within the wood varies, and because of the difficulty associated with measuring pre c i s e l y the area of the spindle-shaped cells, if is assumed that tangential tracheid area is approximated by the prod uct of cell length and width. Similarly® it is assumed that the ray cells are roughly rectangular in shape and their area is equivalent to the product of their height and width. The most important feature regarding the applica tion of this model is whether or not data obtained through secondary tissue analysis can be substituted for data per ta in in g t o th e cambium. T h at is® for example, are T and P 41

(the percent composition of tracheary tissue and ray tis sue, respectively) equivalent to F and B (the percent com position of fusiform and ray initials, respectively ) 2

Clearly the answer to this question depends on the histolo gy of the axes being examined. If a great deal of develop mental change occurred during the differentiation and matu ration of the derivative tissue, then the anatomy of the wood hears little resemblance to that of the cambium® On the other hand, if the developmental changes that occurred were minor® then the general appearance of the wood and cambium should be similar, and the model is applicable.

The structural modification that took place during wood formation is examined for each taxon individually in the respective chapters, and the applicability of the model is discussed in association with these analyses. 42

Figure Is Illustration siioslng method for determining radius of obligue axis in coal ball slab

F ig u re 2z Diagram of cambial cylinder used in determining number of cells in meristem at radius S 43

S m

© Chapter 122

1ESOOS

LEglDODBlDBA&BS

L®roid<88d@ffl-dgid S t ® a s

Based on tie analysis of mature vascular tissues* the cam bium in the lepidodendrids appears to have differentiated in regions contiguous to the primary xylem cylinder (Fig-

31 . fiadial continuity can be observed in some places between metaxylem tracheids and files of secondary elements

(Fig- 3* arrow) suggesting that at least some of the ini tials Here derived from peripheral procambial cells. Hhen viewed in longitudinal section* the transition zone between the primary and secondary xylea is estremely narrow and poorly defined (Fig- U)- Nevertheless* the two types of conducting tissue are easily distinguished from one another by the presence of ray cells in the secondary wood and by differences in the morphology of the tracheids. The outer most metaxylem elements are rather short* with either trun cate ends or blunt tips (Fig. 4* arrows). In contrast* the innermost secondary tracheids are elongate and exhibit extended* gradually tapering cell apices (Fig. 5 ) In some 45 p la ces* the transition zone is characterized fcy a narrow

Cuniserlate?) r e g io n o f sguare to rectangular parenchyma c e l l s (Fig® 4f t h a t a r e s im ila r t o th o s e r e p o r t e d by A rnold

(1 9 4 0 ). The cells are morphologically distinct from those o f th e rays* which tend to be slightly smaller and sore o v a l i n o u t lin e . It is not clear if this tissue Is secon darily derived or if It represents remnants of a sheath of primary parenchyma that surrounded the xylem cylinder prior to secondary development.

fejood structure was examined in seven stems of P a ralvco- p o d ite s* the secondary xylem cylinders of which ranged in radius from 14-40mm. The data from a single representative stem are d e s c rib e d and depicted in this section.Informa tion pertaining t o the other stems is presented in tabular form in Appendix A. The h is t o lo g y of associated e x tr a x y - la r y t is s u e was s tu d ie d in three well-preserved specimens o f Lepidodendron scleroticum and one of l e ridodendron dicentricum,

From a purely guantitative point o f view * the axial sys tem in Paralvcopodites wood i s th e dominant component* comprising between 90 and 95% of the total area in tangen tial sections (Fig. 9 ) . The rem aining 5 to 10% i s d iv id ed between secondary rays (4-9%) and leaf trace tissue (ca.

1%). Except for sporadic zones of "subdivision/ reorganization" (see below)* these levels remain relatively 46

c o a st ant from the first- formed secondary xylem (Fig* 5) to

th e l a s t (Fig- 6 ) -> Despite this apparent developmental

stability in percent composition of th e wood, a n a l y s i s

reveals. several characteristic structural changes that

occur during secondary growth.

The most distinctive pattern of change in the secondary

mood i s the increase in tr a c h e id length-, The first- formed

xylea elements exhibit mean lengths in th e 13-14 mm range

(Fig® 10} - From t h is p o in t in th e wood, tr a c h e id le n g th

increases steadily- In the outer good, the increase in

element length is more moderate (Fig- 10)® In the most

peripheral portions of the secondary xylem, maximum tra

ch eid le n g th s ranged from 24 to 25 mm. The great length of

these cells, in general, conforms to the estimates suggest ed by previous workers (e.g.„ A rn o ld , 194 0b; Eannell, 1942;

F e l i x , 1952) -

A similar change cccurs in the tangential diameter of

the tracheids (Fig- 10)« The width of the first-formed calls generally averages about 85 urn- Toward th e periph ery, there is a consistent increase in cell diameter fol

lowed by a gradual stabilization at approximately 120u i

(Fig® 10). A similar pattern of increasing tangential tra ch eid diam eter in lep id o d en d rid wood was r ep o rted by Ean- n e l l (1942) and F e lix (1952). 47

Incorporating the data for cell size into EQ9 results in the graph shown in Fig® 11- The observed pattern of change in cell number is inferpretted as follows® Early in devel opments, the cambium was characterized by a relatively large number of fusiform initials® As mood production continued and the cambium mas displaced radially* the number of ini tials decreased steadily® at later stages in secondary development* the number of fusiform initials became rela tively stable®

There is no evidence in Paralvcopodites that additional fusiform initials were systematically produced by the anticlinal division of pre-existing cells® A phenomenon was observed* however* ahich may have provided a mechanism for the production of new fusiform initials® In stems characterized by large amounts of secondary xylem* regions of localized cellular subdivision and apparent reorganiza tion are observed. Such zones are similar in morphology to those reported by Williamson (1872a* b) and Scott (1920).

In cross section the zones appear as small interuptions or irregularities in the radial arrangement of contiguous tra cheid files (Fig® 7)® normal tracheids are succeeded radi ally by cells that are much smaller in diameter; as many as five of the small cells may occupy the tangential width of the preceding tracheid® The ceils are relatively short* fusiform in shape* and exhibit walls thickened in a scalarifora pattern (Fig. 8 ). Thus* they resemble minute tra cheids. She cells are arranged in radial files of variable length; most of the files contain only a feu cells and ter minate irregularly at short distances from the point of initiation. Less frequently* the files are succeeded lay loss of tracheids that are interposed between preexisting oses (Fig. 7). Occasionally a large parenchymatous ray is

initiated at the site where the “interruption 58 occurs (Fig.

7* arrow). The histology of these zones in the wood sug gests that fusiform initials sporadically subdivided to form a large number of minute cells with meristematic potential. Although most of the new cells were subsequent ly lost from the cambium, some were converted to fusiform or ray initials. This outcome is displayed in Fig. 12, which depicts data from an analysis of a series of tangen tial sections through a zone of subdivision. It is appar ent that an abrupt increase in the number of fusiform in i tials occurs just beyond the zone of reorganization.

In-depth analysis of the ray system in P a r a l v co p o d ites is hampered by poor preservation of th e cells* particularly i a the more peripheral portions of t h e wood. Only one of the seven stems examined exhibited a d e q u a te cellular pres e r v a tio n to permit detailed study; three other stems were submitted to partial analysis. In all cases* the shape and overall size of the cells remained constant from the 49 first-formed wood to the Ia si* The data® however® were regarded as b ein g insufficient to alios definitive state ments regarding quantitative features of ray initial d e v e l opment.

At the periphery of the woody cylinder, the tangential and radial diameters of the tracheids often decreases rath er abruptly {Fig. 13). In a d d itio n , the tangential w idth of the rays increases,, and ray cells merge with cells of the parenchymatous sheath that surrounds the secondary xylem. In transverse view {Fig. 13)® the transition zone between the secondary tracheids and the cells of the sheath appears narrow and well defined. Analysis of tangential sections® however, shows that there is a gradual histologi cal progression from tracheid to parenchyma cell. Normal tracheids are succeeded radially by parenchyma cells arranged into axially oriented zones or patches (Fig. 14).

In general® the shape of these patches conforms to the out line of the preceding tracheid (compare fig. 14® 15 at arrows)- In addition® th e innermost sheafh parenchyma cells are often characterized by w a lls thickened in a scalarifors or reticulate pattern (F ig . 1 6 ). More p erip h era l sheath cells® however® exhibit a normal pareachymatous appearance (Fig. 17). On the basis of these data® it is suggested that® at the end of secondary growth® initials of the determinate cambium subdivided forming a narrow band of s m a ll meris teaa tic c e lls. These initials functioned for a limited period of tine producing cells that differentiated into small tracheid-like cells. Ultimately the minute i n i

tials ceased to d iv id e and became parenchymatous in a p p e a r-

ciLisi ceo 51

P la te J

Lepidodendrid stems-—Fig- 3-8

Pig® 3® Transverse section of prlmary/secondar y xylem tran s i t io@ zone in lepidodendron illustrating tr a c h e id f i l e t h a t i s r a d i a l l y c o n tin u o u s a c r o s s zone® C.B® 551 C b o t #3® x 160® Fig® 4® Tangential section of primary/secondary xylem at transition zone shotting metaxylem (arrows) and abundant parenchyma® C.B. 7294 B s i d e #16® x 110® Fig® 5® Tangential section of inner wood o f P aralvcopodite s showing l e a f t r a c e af upper left® C®B® 7294 B s id e #13® x 110®

Fig®«•' 6 ® Tangential section of outer wood of Paralycopoditesimnmn . HIlllKIl nr showing leaf trace at upper right® Note distinctive scalar- Iform thickenings on tracheid Halls® C.B® 72 94 B s id e #2® x 110® Fig® 7® Transverse section of "subdivision/ reorgani z a t i o n " zone® Outer portion of wood is toward top of fig ure® Note large ray initiated at zone (arrow)® C®B 104 A #2- x 110® Fig® 8® Tangential section of "subdivision/ reorganization" zone in Paralycopodites show ing intervening tracheid between two subdivision zones. C.B 104 k s id e #14® x 310. PLATE I 52 53

Fig- 9-10 — Develop mental Data for lepidodendrid Stems

9 : Graph showing percent composition of tracheid, ray and leaf trace versus percent wood radius. Note general stability of pattern throughout wood. Tracheid (JO ; ray I ii) ; leaf trace

10: Grapn of tracheid length and mean width versus percent wood radius. Note increase in cell length from inner tc outer wood. Vertical tars correspond to one standard deviation above and below mean. Length |J|) ; width (O ) *> {%) smcm aooM RCED ZE (MM) E IZ S TRACHEID

AGNIL RA (%) AREA TANGENTIAL 100 tfl ■Sr 55

Fig. 11-12 — Developmental Data for Lepidodendrid Stems.

1 i; Graph of tracheid number versus percent uood radius. Note reduction in number of tracheids from inner to cuter bocd.

12: Graph of tracheid number versus percent wocd radius for stem exhibiting zone of “subdivi sion”. Note sharp increase in number cf tra cheids associated i»itfc occurrence of zone in middle wood. NUMBER OF TRACHEIDS (CELLS) NUMBER NUMBER OF TRACHEIDS (CELLS)

WOOD RADIUS (%) 51

P l a t s I I

Lepidodendrid Stems—Fig. 13-17

Fig. 13. Transverse section of peripheral wood and adjacent extraxylary tissue® Note general absence of radial s e r i a - tio n In latter indicating presence of nnifacial cambium. CoBo 225 & Mo x 120. F ig . 14—17. Series of tangential sections through peripheral aood and adjacent extraxylary tissue. Fig. 14. Section showing fr a c h e id tip at arros and l a r g e multiseriate r a y s . C.B. 225 B5 s id e b #8 . x 120. Fig.. 15. Section showing zone of parenchyma that conforms to outline of tracheid in Fig. 14 (arroe) . Note general increase in ray/sheath parenchyma. C®B. 225 B5 side B #9. n 120® Fig. 16® Section showing scalarifora and reticulate

thickenings on walls of post mer1 s tematic sheath parenchyma. G. B. 225 B4 side a #41. x 160. Fig® 17. Section shotting sheath parenchyma. C. B. 225 B5 s i d e bill, x 160. PLATE I I 58 The disposition of mature vascular tissue in stig m a ria n

ares suggests that the cambium differentiated in"regions

c l o s e l y adjacent to the primacy xylem® I n cross section* a

distinction between th e o u te r metaxylem and the innermost secondary xylem can not be made (Fig- 18} indicating that

the t'so tissues may have been derived from the sais

merisfcematic cells® This suggestion is further strength

ened by the structural- similarity of the two tissues in

longitudinal view (F ig- 19)* where the only consistent dif

ference is the presence of rays in th e se c o n d a ry xylem .

Differences are also present in the tangential diameter of

the tr a c h e id s and the p attern o f scalariform pitting, b u t

these tend to be subtle and sporadic® Thus* the first-

formed initials of the vascular cambium in Stigmaria were

probably peripheral cells of the procambial cylinder rather

than meristematic cells that differentiated de novo.

The wood of stigmaria was examined in a total of five

axes in which th e ra d iu s o f th e secondary xylem cylinders ra n g e d from about 8 to 18 mm. Data from a single represen

tative axis are examined in this section, and information

o b ta in e d from analysis of the other specimens is included

in tabular form in Appendix B. The s tr u c tu r e o f th e l a s t -

formed wood and e xtraxylary tissues was determined from the study of a single well-preserved axis. 60

The a x ia l system in Stiqia atria wood is composed e n t ir e ly

o f e lo a g ate tracheids and is quantitatively th e dominant

cellular component o f th e t is s u e . Tracheids generally

account for between 80 and 85% of the total area in tangen

tial wood sections (Fig. 2 4 ). The area occupied by rays

associated with the rootlet traces ranges fro® 1 0 to 151*

and the wood ray system makes up the remaining 5 to 10% of

the area. Except for slightly greater amounts of ray tis

sue in the outer wood and the sporadic zones of subdivision

and reorganization (described below)® these percentages remain relatively constant through the entire thickness of

the xylem cylinder (Fig. 24).

Perhaps the most characteristic features of stigmarian

wood are the large rays associated with the rootlet traces,

which heretofore are referred to as RT (rootlet trace) rays

(Fig. 20, 21). In tangential section these rays typically

appear as pyriform lacunae. Small, distorted parenchyma i cells often line the cavity, and the trace to the rootlet occupies the broad basal-most portion of the ray. To sim

plify calculating the area of the HI rays (Art), it was

assumed that the shape of the rays conformed to the outline

o f an isosceles triangle® The following formula was used

to determine RT ray area:

a x y (a/2)2 + b2

2 61

where a = width of the base of the ray# and

h = height of the ray®

Mean HI ray area for each section was determined based on a sample size of no less than five rays® As shown in

Fig® 25# the size of the rays increases fro© the first- formed wood to the last® Shis enlargement is primarily a r e s u l t of an i n c r e a s e in th e uidfch o f th e ra y (Fig® 20#

21)® The broadening of the ray suggests that there was an increase in the size and/or number of the component ray cells signifying the multiplication and/or enlargement of the respective cambial initials. More definitive state ments regarding the development of the RT rays cannot be made in view of the generally poor preservation of the ray c e l l s .

A progressive pattern of enlargement occurs in the length and tangential diameter of the tracheids from the inner to the outer wood. The first-formed secondary ele ments exhibit mean lengths in the 8-10 mm range and widths of approximately 60 ur (Fig® 26)® At progressively larger radii there is a marked increase in the size of the cells# and in the outer parts of the wood tracheid length general ly ranges between 20 and 25 mo (Fig® 26)® Tracheary ele ment width similarly increases from the inner to the outer wood# but# in contrast to cell length# it fends to become stabilized at more intermediate radii* The uidesi cells are usually found in th e o u te r wood where d iam eters a re typically in the 125 urn range (Fig* 26). These distinctive p a tte r n s of tracheid enlargement in the good are indicative of developmental trends in the cambium and signify a pro gressive increase in the size of the fu sifo rm i n i t i a l s *

Assuming that the tangential area of the individual tra cheids approximates that of the initials from ahicb they

Mere derived (see Discussion ) g the data can be incorporated i n t o EQ9 to provide an estimate of the number of ca m tia l initials at each radius* The resulting graph (F ig . 27) shows that a relatively large number of fusiform initials sere present in the first-formed cambium, as in the stems.

The number dropped steadily until a point was reached where the number of fusiform initials in the cambium stabilized*

Further centripetal production of cells increased the radi us and circumference of the cambium, b u t little net change o c c u rre d in th e number of initials in the meristem.

S tig m a r ia apparently possessed a sporadic mechanism t h a t seems to have in c r e a s e d th e number o f fu sifo rm i n i t i a l s in th e developing cambium. &t what appear to be ran dom positioos in the wood, the radial arrangement of one or several adjacent tracheid files is interrupted by lo c a liz e d wnestsn of smaller cells (Fig. 22). These cells generally have the appearance of minute tracheids (Fig. 23) and are 63 arranged la radial eobs. the majority of the files termi nate close to their point of initiation (Fig. 22), but some are succeeded by rows of tracheids or rays- It is suggest ed that these zones represent sites at which fusifora ini tials subdivided- Most of the meristematic products formed in this process Mere ultimately lost from the cambium, but others enlarged and continued to function as asa camfcial i n i t i a l s .

Study of the ray system in Stigmaria Is made difficult by the poor preservation of the cells- B ays, particularly those in the outer portion of the wood, resemble la r g e lacunae between the tracheids (Fig. 23). In tangential view, the boundary between the rays and tracheids is easily reco g n ized on th e b a s is of the unusual appearance o f th e sectioned cross-field pits. In only one of the stems investigated was the preservation of the c e l l s s u f f i c i e n t to allow a complete analysis o f the ray component, and cell size appeared to remain relatively constant throughout the wood. The general absence of specimens exhibiting a suita bly preserved ray system precludes a guantitative analysis of the development of the ray component In Stigmaria.

At the outer margin of the wood, the tracheids abut with th e more peripheral parenchymatous tissues (Fig. 28).

Serial tangential sections reveal that the progression from tracheid to parenchyma cell is gradual. Normal tracheids (F ig . 29) are succeeded by ssall-diameter* sinuous cells sitfe sails differentially, thickened in a scalariform pat te r a (F ig , 3 0 ) • She cells are organized into groups t h a t conform to the outline of the preceding tr a c h e id . Secon dary rays are recognizable throughout this zone (F ig. 30*

31* at arrows) =» More peripherally* the tracheid-like c e l l s assume an ovoid or rectangular shape* and the scalarifora pattern of the walls is lo st.. The cells ultimately appear as normal ground parenchyma (Fig.. 3 1 ). 65

P l a t e I I I

Stigmaria—-gig., 18-23

Fig- 1 8. Transverse section of primary/second ar y xylem transition gone showing radial continuity between cells o£ t bo tis s u e s ® P o o rly p re s e rv e d p ith located at bottom of figure® C«B® 822 D hot #10a® x 110® Fig® 19® Slightly oblique tangential section of primary/secondary xyle® boundary® Outer m etaxyles is at top of figure and inner se c o n d a ry xylem is at bottom® Note wood r a y s a t arrows® C®B® Q1U9 A s i d e #18® x 110® Fig® 20® Tangential section of inner aood shoeing narros rootlet trace {RT) ray (arrow)® C® B® 8521 B side #18- x 20® Fig® 21® Section similar to Fig® 20 but obtained from outer aood® Note extremely broad RT ray and general absence of cellular preservation within ray® C®B® 8521 B side #2® x 20® Fig® 22® Transverse section o f wsubdivision/reorganization” zone showing limited later a l extent of region. Figure is o r i e n t e d such that periphery o £ a x is i s at top® C.B® 822 D bob #10c® x 110® Fig® 23® Tangential section of "subdivision/reorganization" zone shoving subdivided tracheid between two normal tracheids. Note large wood ray lacuna at arrow® C® £. 8 5 21 B s i d e #7® x

120® PLATE I I I 66 67

Fig* 24-25 — Developmental Data for Stigmaria

24'. G raph of percent composition versus percent wood r a d iu s i FIGDISC*Note general statility in pat tern from inner to outer wood., Tracheid (A); ray (H ) ; rootlet trace ray C#)»

2 5 : Graph of mean BT ray area versus percent wood radius* Note general increase in size of ray from inner to outer wood* Fertical cars repre sent one standard deviation above and below mean* 4 0 6 0 WOOD RADIUS (%)

4 0 6 0 WOOD R A D IU S (%) 69

Fig. 26-21 —■ Developmental Data for Stigmaria

26: Graph of tracheid length and mean width versus percent wood radius. Note that both length and mean aidth increase markedly at progressively greater radii. Length (A) ; width {#). Verti cal lars represent one standard deviation above and below mean.

27: Graph of number of tracheids versus percent wood radius. Note decrease and stabilization in number of c e l l s from in n e r to c u te r wood. © TRACHEID SIZE (MM) O MOOD RADIUS (%) © © m »-* »-* NJ W o o o NUMBER OF NUMBER TRACHEIDS (CELLS) <0 o o O' A o WOOD RADIUS (96) 71

P l a t e IV

Stigmaria— Fig. 28-31

Fig. 28. Transverse section of peripheral wood and adjacent extraxylary tissue,, Hote general absence of radial align ment in cells of extrasylary zone. C.B. 822 D bot #10b. x 110. Fig. 29-31. Tangential series through peripheral wood and extraxylary tissue. Fig. 29. Section through outer wood shoMing tracheids and rays. C.B. 822 02 side #34. x 110. Fig. 30. Section through post-meristerna tic sheath. Note stunted tracheid-like cells with scalarifora thickenings and wood ray {arrow) . C.B. 822 02 side #16. x 110. Fig. 31. Section through parenchymatous portion of sheath show ing large rectangular cells presumably derived from subdi vided fusiform initials and rays {arrow). C.B® 822 D2 side #11. x 110. L T IV PLATE

to 7 3

SPHEBOPHgUL&&BS

A well-marked structural distinction is present between the primary and secondary xylem ia Sphenophvllum plurifoliatum (Fig. 32, 34) . The walls of the metaxylem tracheids are characterized by scalariform secondary thickenings

(Fig® 33) or by a b u n d a n t s c a l a r i f o r a p i t s (F ig . 3 5 ). No trace of vitalizatioa is present in the tissue® In the secondary xylem, the tracheids are characterized by closely spaced bordered pits on the radial walls (Fig® 37, 39, 40) and an unusual horizontal ray system is present (Fig. 36,

37, 39, 40)® Situated between the primary and secondary xylem in the interfascicular region is a narrow parenchyma tous layer (Fig. 33-35). In this zone, the cells generally appear square to rectangular in tangential view (Fig. 33) and are tangentially flattened in radial (Fig. 35) and cross sections (Fig. 34). Many of the cells contain a brownish, presumably ergastic substance. It is likely that this tissue represents a portion of the stelar parenchyma

(pericycle or phloem parenchyma) from which the cambial initials differentiated. Some of the cells exhibit small, horizontal peg-like extensions (Fig. 35) similar to those of the rays, suggesting that the cells may have given rise directly to the ray initials.

In Sphenophvllum. the interfascicular secondary xylem comprises a larger percentage of the total weed area than the fascicular segment,, especially in small stems {Fig*

32J - Moreover*, in the innermost regions this wood tends to be better preserved than the fascicular, and the distinc tion between parenchyma cells and tracheids is more appar ent® For these reasons, analysis of the wood in this taxon focuses exclusively on the structure and development of the interfascicular wood. Data was collected from a total of five stems that ranged In diameter from 1.8 to h.9 mm®

Thickness of the secondary xylem in these specimens ranged from 1® 0 to 3®8 mm. In keeping with the general concept that these plants exhibited determinate growth and the majority of the preserved specimens were developmental!y mature (Eggert and Gaunt, 1973), it is assumed that each of the stems examined in this study had ceased lateral growth well before they were buried and preserved® The results obtained from the study of a single representative axis are presented in this section. Data pertaining to the ether four stems are depicted in tabular form in appendix C.

The axial system in Sphenophvllum wood consists entire ly of elongate tracheids arranged In both radial files and concentric rings (Fig. 32)» Because of variability In the ray component within a concentric ring, accurate estimates of percent ray area and percent tracheid area cannot be made. Tangential sections through the region between con centric rings of elements (Fig. 3 6) suggest the percent ray 75

area in the wood was in excess of 3OIL, Jn c o n t r a s t , s e c 

tions through the median longitudinal plane o f th e tr a 

c h e id s (Fig® 37| indicate that the rajs comprised less than

58 of th e t o t a l wood area® T h is variability is a result of

dimorphism in the ray cells between and within adjacent

concentric xylem rings®

The length and tangential diameter of the tracheids

changes dramatically from the first-formed wood to near the

periphery (Fig® 44}. In the early wood the elements range

from about 13 to 15 mo long, and the aidth is usually in

th e 120 t c 140 urn range® Element length increases steadily

at progressively greater radii*, and near the periphery, the

mean length is in excess of 25 mm. Given the apparent con

sta n c y in the rate of increase, maximum cell length is

observed in the last-formed wood. Similarly, the increase

in t r a c h e i d diameter is steady (Fig. 4 4 } , but it appears to

re a c h a maximum a t more in te r m e d ia te r e g io n s i n th e wood.

The maximum width, which typically averages around 160 urn,

is usually maintained from this intermediate point to the

periphery of the xylem cylinder®

The unusual construction of the horizontal ray system

has been alluded to above. The apparent radial discontinu

ity between cells indicates that the interfascicular wood o f Sphenophvllum was characterized by a true ray s y ste m .

The files are typically arrangeda s individual "t-shaped” 76 cells that a lt e r n a t e with small groups of upright cells

(Fig<> 38-40)® The t - c e l is appear to represeat upright cells with a single radially oriented outgrowth or process ex ten d in g be twee a adjacent tracheids in a ring® The upright cells are radially continuous with th e t - c e l l s and occupy the regions between two tracheids o f one ring and the contiguous pair in the succeeding ring (Fig® 38, 39)®

It is clear that the upright cells and those with radial processes constitute parts of the same file since the height of the cells remains relatively constant between cells (Fig® 39, 40)® Furthermore, where horizontal divi sion of a cell occurs, the new cross wall is retained in the more peripheral cells (Fig® 4 0 ) . Outside of a file the height of the cells varies, and a recognizable pattern is not apparent (Fig® 36)® The cells are approlimately 30 urn wide® The horizontal processes, which are radially cylin d r i c a l or conical, are as lo n g as the adjacent tracheids are wide and extend to the succeeding ray cell in the file

(Fig® 38-40)® Sectioned transversely, the processes appear ovoid with dimensions of about 20 us by 35 um (Fig® 37)®

Since a cambial zone was not preserved in any of the specimens examined, and since significant structural change appear to have taken place during wood formation, cambial development can n o t be studied by direct analysis of the wood® T hus, f o r Sphenophvllum a hypothetical developmen 77 tal scenario is proposed that attempts to explain the vari ous structural properties of the »ood- Using this account as a model, the histological organization of the cambium is inferred.. In general* radial cell enlargement seems to he a significant phenomenon in the development of secondary tracheids (lilson, 1963). Such is also likely to have been the case in Sphenophvllum,, where variability in this parameter is often observed between cells in a radial file.,

Since the inner portions of the wood in this plant were occupied by a solid core of incompressible lignified tis sue, it is likely that the greatest part of the tracheid broadening process occurred centrifugaily. It is envi sioned that a localized outgrosfch developed on the outer tangential aall of the differentiating ray cell as tracheid enlargement began. Continued radial enlargement of the developing tracheid was accompanied by the centrifugal elongation of this outgrowth such that, at ma turity, the ray cell exhibited the distinctive ”t-shapedn morphology.

If this developmental scheme accurately depicts ray cell development in Sphenophfilms* then the majority of the

“>t-ceXls10 should be oriented with the radial outgrowth directed toward the outside of the stem. A cursory analy sis of the wood reveals this to be the case {e.g„. Fig. 39,

40). As the radial diameter of the tracheids increased, the radius of the stem became larger, and thus the circum- 78 fe r e n c e of the axis increase do This radial enlargement in the differentiating tracheids was accompanied by a slight increase in the tangential diameter of the cells such that adjacent tracheids came info contact with one another along their radial B a l l s . One of the final phases of development that seems to have affected the appearance of the wood was the rounding of the corners in the tracheids. This process resulted in the formation of elongates, axial intercellular s p a c e s b e tBeen the elements that Mere apparently filled as a result of enlargement o f the upright ray cells® The developmental changes that occurred in the shape and s i z e of the ray cells during ®ocd differentiation often mask the radial arrangement of the cells in the interstices when viewed in cross sections (Fig® 38).

In accordance with this scheme for secondary xylem development, the cambium in the interfascicular region of

Sphenophvllum appears to have been composed of alternating zones of individual fusiform initials and axially elongate hands of ray initials® She morphology of the ray cells suggests that the initials were rectangular in tangential view® The height of the initials appears to have been variable since this dimension in the ray cells shows little constancy between files® Host o f the upright ray cells e x h i b i t tangential w id th s of approximately 30 um® Although some degree of enlargement may have taken place in t h i s 79 parameter with the form ation of the gaps between concentric r i n g s of tracheids, f o r th e sahe o f t h i s a n a ly s is i t i s assumed that the a id th o f th e r a j i n i t i a l s was 30 u<» The pattern of the horizontal "peg® portion of the raj cells in tangential wood sections (fig. 37) suggests that the ray initials were arranged in a uniseriate or h i s e r i a t e p a t tern,, Based on this p r e s umptive organization of the ray component in the cambium and the arrangement of the tra c h e id s nith respect to the rays in the wood, individual fusiform initials were probably isolated from one a n o th e r by e lo n g a te zones of ray initials. Since tracheids in a concentric ring are u s u a lly in contact with one another in th e mature wood, the tangential a i d t h of the fusiform ini tials must have been slightly smaller than than that of the corresponding tracheids. Despite these apparent chang es during differentiation, there is no evidence to suggest th a t the le n g th of the fusiform initials differed signif i- ca n tly from t h a t of the tracheids.

In i t s p r e s e n t form. Equation No. 9 c an n o t be used i n a n a ly z in g th e axial component in the cambium o f Scheno- phyHum , allowances must be made for the fact t h a t o n ly one segment of the interfascicular wood is being examined.

M oreover, since the structure of th e wood apparently does not directly reflect that of th e cambium, several of the parameters in the equation oust be redefined. Figure 46 80 depicts a standardized arrangemeat of the different xyle® components in a cross section of Srhenophy11 urn. By defini tio n *

a lp h a = ,77./3 and

Ps = -the linear distance between the concent”

ric arc of tracheids and the focal point of

the arc (i.e. e the opposite protoxylen pole).

Thus* for Sphenophyllum. the area of the interfascicular cambium is defined as

(11)

7T 1 Sd I H

Incorporating the modifications of Equation No. 11 info

Equation No. 9 yields

( 12)

F x Aic Nf ------— I f X Nf

For Sphenophvllum the number c.£ tracheid files (Nfl) in the interfascicular zone at any given radius (Ps) is d e fin e d by

(13)

V x Ps N fl = ------3 X Wt

where Wt = tracheid width 81

S in c e individual files of tracheids alternate s i t b ra y

file s ® Nfl for the tracheids is equal to N fl for the rays

(assuming a uni seriate condition in the ray system!.» Thus

the area occupied by th e ray i n i t i a l s (Ar) in the cambium

is defined as

fir = N fl x I r

where Ir = aidth of the ray initial (by convention

in t h i s a n a l y s i s I r = Q® 03 1 1 } »

Conversely® the area occupied by the fusiform initials {Af)

in th e cambium i s

Af = Aic - Ar

Thus® the p ercen t co m p o sitio n o f th e cambium occupied by

the fusiform initials (F) is

(14)

F = A f/A ic

Finally® since the fusiform initials appear t o have been

arranged in isolated files® the width of the initials (if) can be calculated by

(15)

if = Af/Nfl

Substituting Equation No® 13-15 for parameters in EQ12 and assuming that If = It (see discussion) yields:

(16) 82 Me Hf « ------I t x it

Thus* despite the fact that there appear to ha we been sig

nificant structural changes during differentiation, EQ16

indicates that parameters of the mature wood can be used to

study. i cambial development sk in Sphenophyllum®—m ■rwiw»*g»wa»

I lie orp era ting the data obtained in the analysis of the

wood into Equation Ho® 16 yields the graph shown in Fig®

45® It can be seen that the number of fusiform initials

rem ained relatively constant from the first-farmed wood to

the last® This suggests the absence of multiplicative

divisions in the interfascicular cambium, confirming earli

er speculation on this topic (Cichan and Taylor® 1982)®

Moreover® if indicates that the gradual enlargement o f th e

i n i t i a l s was sufficient to accommodate the increasing cir

cumference of the cambium.

In most of the stems, tangential width of the tr a c h e id s

appears to remain constant up to the point at which the

file terminates (Fig® 32)® In some of the files, however,

the size of the outermost two or three tracheids Is reduced

(Fig® 41)® Accompanying this reduction in size is a gradu

al increase in the tangential width of the ray component

(Fig. 42). Presumably the small tracheid-like cells repre sent the modified remnants of the fusiform inifals or their

last-formed derivatives in th e d e te r m in a te cambium® 83

Bordering the secondary xyle.s Is a moderately broad zone of tissue which appears to represent the primary phloea

(Fig. 41) » Conclusive evidence that this tissue is phloem* honever* is presently lacking® The cells of this estrasy- lary zone are morphologically distinct from the outermost ray cells^ on the average* ray cells in this region are less than 140 us long and exhibit a radial diameter of approximately 15-20 um ' (Fig* 42)® Cells of the adjacent eztraxylary zone are usually lore than 500 um long litfe radial widths of about 50 um. In addition* the latter cells tend to appear slightly swollen at their ends* and the endaalls are horizontal or slightly oblique (Fig. 43).

She transition between these two cell types is abrupt* and there is no evidence of cells that are intermediate in mor p h o lo g y . 84

S la te ¥

Sphenophyllum— Fig. 32-37

F ig . 3 2 . Transverse section of stem shoeing triarch primary jcylem (P) g fascicular wood (F) and i n t e r f a s c i c u l a r wood (IF)o C.B. 1033 H6 i2» x 20. Fig. 33. Tangential section of primary xylea showing tracheids with scalariform w all thickenings. Note parenchyma at primary/secondary xylea boundary (arrow). C.B. 8525 D1 side §2. x 190. Fig. 34. Transverse section of primary/secondary x y le a transition zone show ing thin layer of parenchyma at boundary (arrows). C.B. 8525 D1 side #9. x 110. Fig. 35. Eadial section of primary xylea showing element a ith oval bordered pits. Note parenchyma at primary/secondary boundary (arrow). C.B® 8525 C side #23. x 110. Fig. 36. Tangential section of wood at ju n c tio n between adjacent concentric rings of tracheids. Note upright ray parenchyma cells. C.E. 8525 C side #71. s 120. Fig. 37- Tangential section of wood through individual concentric trach eid ring. Compare appearance of ray cells with those in Fig. 36. C.B- 8525 C side #40. x 120. PLATE V 85 86

P l a t e VI

Sphenophyllua— Fig.. 38-43

Fig® 38® Transverse section of wood shoving arrangement of tracheids and ray system components® Arrow illustrates radially oriented "peg" portion of cell extending from one group of cells to adjacent group® Figure is oriented so that outer wood i s a t top® C. E® 6620 B1 fcot #41® s. 160® Fig® 39® Radial section of vood shoving groups of upright cells in interstices between concentric rings of tracheids® Mote low horizontal processes extending radially and con necting groups of upright cells. Figure is oriented so that outer wood is at left® €®B® 8525 C side #23® s 110. Fig® 4 0® Tangential section similar to Fig® 39 showing evidence of horizontal subdivision of ray cells within radial file of cells (arrows). C. B. 209 C3 side #1® x 130® Fig® 41® Transverse section of stem showing outer vood and adjacent extraxylary tissue® Note sharp reduction in size of outer m ost tracheids. Arrow illustrates zone of large d ia m e te r cells that possibly represent phloem. C.B® 209 B2 t o t #11. x 120. Fig. 42-43. Tangential series through o u te rm o s t wood and adjacent extrazylary tissue. Fig. 42. S e c tio n through outer wood showing tracheids and intervening rays. C.B. 209 D2 s id e #53. x 120. Fig. 43. Section through par enchymatous extraxylary tissue illustrated in Fig. 41. C.B. 209 D2 s id e #55. x 120. PLATE VI 87 88

Fig. 44-45 — Developmental Data for Sphenoph yllum

44: Graph of tr a c h e i d le n g th and mean w idth v e rsu s percent wood radius- Note consistent increase in tracheid length from inner wood to cuter wooa and apparent stabilization of ceil width at intermediate radii- Vertical tars represent one standard deviation above and below mean- le n g th (A) ; width (®),

45: Graph of number of tracheids versus percent wood radius. Note stabilization in number of cells at progressively greater radii- TRACHEID NUMBER (CELLS) TRACHEID SIZE (MM) o o 5 7 . 0 NJ K> O un w o o OD AIS %) (% RADIUS WOOD

CD 90

46: Standardized stem anatomy in Sphenophylluc. Center triangle represents primary xylem sur rounded by alternating segments of fascicular (F) and interfascicular {IF) »ood- Angle of primary xylem zones ( a ) equals 60 degrees. See text for details., 91 IQSlSB^I&gg

Istharamtis aoaaaais

Analysis of nature vascular tissues suggests tliat e a r ly in development the cambium in A rthropitys communis consisted of two distinct components corresponding to the fascicular and interfascicular regions of the wood- In the fascicular zone* the primary body is characterized by cylindrical* axially oriented protosylem lacunae ( c a r i a a l canals) sur rounded by elongate thick-w alled parenchyma c e lls (F ig-

47). In cross section* these parenchyma cells resemble tracheary elements* but longitudinal sections reveal that* unlike tracheids* endaalls of the cells are horizontal and the lateral walls are not differentially thickened (Fig-

48) . The metaxylem appears to be confined to a narrow zone directly adjacent to and just beyond the protoxylem lacunae

(Fig- 47* 48)a Ihe tracheary elements are elongate with gradually tapering ends* and the tangential and radial walls are secondarily thickened in a scalariform pattern

(Fig- 48)- Thick-walled elongate parenchyma c e lls which gradually merge with the in te rfascic u lar ground parenchyma are present laterally on both s i d e s of the metaxylem zone-

Metaxylem cells and associated parenchyma are succeeded radially by elements of the secondary xylem. Files of sec ondary tracheids are contiguous to both metaxylem tracheids and parenchyma cells (Fig- 47)* suggesting that camtial 92 initials were formed directly by the conversion of procambial cells® Ray initials sere apparently produced by the horizontal subdivision of metaxylem parenchyma cells.

Using the terminology established in the study of e x t a n t

p l a n t s (Barghoorn* 1940? Bannan* 1950* 1951)* the r a y s cl the fascicular zone should be referred to as "primary

rays." To distinguish then from the broad rays between the primary vascular bundles* the former are referred to as

"fascicular rays" in this work. Ihere i s l i t t l e d is tin c -

tion between the last-formed metaxylem and the first-formed s e c o n d a ry xylem. The only consistent difference between

the two tis s u e s appears to be th e pattern of secondary thickening on the tracheid walls. In the primary xylem*

the elements are differentially thickened on loth the tan

gential and radial walls (Fig. 48); in the secondary xylem

only the radial walls are differentially thickened. Thus* the d ifferen ce between the two xylem types i s apparent only

in tangential wood sections.

The interfascicular zone o f the primary tody i s composed o f parenchyma cells that ace rectangular or more or less isodiametric in outline {Fig. 4 9 ) „ accompanying the shift from primary to secondary growth there is a gradual change in the morphology of the cells and a distinctive horizontal

arrangement becomes apparent (Fig. 49) . Cells adjacent to

the fa sc ic u la r zone become a x ia lly elongate and those at 93 d eeper p o sitio n s in the ray become isodiametric os h o riz o n tally elongate (Fig- 50® 59)- The gradual change in the morphology o£ the tissue suggests that the interfascicular cambial i n i t i a l s were derived from primary parenchyma cells in w hich meristematic p o t e n t i a l Has retained.

Wood structure was analyzed in a total of sir specimens that ranged in outside diameter from 50 to 82 mm. thick ness of the secondary ‘xylem cylinder ranged from 13 to 24 mm. In each of the stems® however® the outline of the cut e r surface was irregular suggesting that some of the more peripheral portions of the wood had been abraded prior to fossilization. Thus® in life® the thickness of the woody cylinder in each of the specimens was probably greater than that measured in the fossil. Quantitative d a ta obtained in the analysis of a single representative specimen are included in these results. Information pertaining to the other specimens are presented In tabular form in Appendix

One of the distinct features of jU communis wood i s the alternating fascicular and interfascicular regions.

The former zone is composed of elongate tracheids and a well-developed horizontal ray system; the latter is made up exclusively of parenchyma c e l l s (Fig. 55-58). An analysis of the percent composition of the wood shows that in the inner regions the in terfascicular ray occupies more than 94 o n e - h a lf th e t o t a l tangential a r e a (Fig. 51). T h is p e r centage drops dramatically as the radius increases and the fascicular segment broadens. Ultimately, the general organization of the tissue stabilizes* At this point, the fascicular wood comprises about 90s! of the tangential area and the interfascicular segment comprises the remaining 1 0 1

(F ig . 51) *

la the fascicular region, the axial system accounts for approximately 60% of the total tangential area in the outer wood (Fig. 51) and is composed entirely o f elongate tra cheids* In the first-formed secondary xylem the tracheids tend to be relatively short with lengths that average in the 4 to 5 am range (Fig. 52). The tangential width o f the cells in this zone averages about 30 um (Fig. 52). At suc cessively greater distances from the primary xylem, secon dary tracheid size increases, steeply at first and then more gradually. Maximum lengths are observed in the outer wood where the ceils measure between 6.5 and 7.5 mm (Fig-

52) - Similarly, the maximum tangential diameter o f th e elements generally occurs near the periphery of the weed and usually averages about 40 um (Fig. 52). Shen in d iv id u al files of tracheids are followed from th e inner to the outer wood the increase in size is gradual and progressive

(Fig. 55-57). There is no evidence of periodic reductions in the length of the cells resulting from subdivision of 95 the fusiform in it ia ls i n th e cambium. Assuming that the length and width of the tracheids did not change s i g n i f i c a n tly during differentiation, these measurements can he utilized in E guation No. 9 to examine developmental ch an g es i n cam hial structure. Figure 53 shows that the number of fusiform initials in the cambium increased early In d evel opment, tout gradually stabilized as the xylem cylinder became thicker. During the later stages of development there was apparently l i t t l e n et in c r e a s e in the number o f fusiform cambial cells. Analysis of the wood suggests th a t the production of new fusiform cambial cells early in wood development resulted not from multiplicative divisions of preexisting cells, but, rather, by the conversion of ray initials to fusiform initials. In the inner wood, the boundary between the interfascicular zone and the fascicu lar segment is characterized by axially elongate parenchyma cells (Fig. 59). At progressively greater radii, these cells are gradually succeeded by tracheids (Fig. 50,

59-61), suggesting t h a t interfascicular ray initials were the source of the nei fusiform initials. This process seems to have constituted the principle mechanism by which th e w idth o f th e interfascicular zone was reduced d u rin g wood development. In c r o s s s e c t io n s , new f i l e s of tra cheids that appear to originate de novo within or near the interfascicular zone (Fig. 50) actually represent por 96 tions of transforming files; there is a gradual centrifugal increase in cell length associated with the conversions and thus only the more peripheral parts o f the file can he seen at a particular transverse level® A similar pattern o f cell arrangement in the wood was described for files of tracheids in Sphenophyllum (Cichan and 2aylor, 1982). The g ra d u a l conversion of the rectangular interfascicular ray i n i t i a l s to the elongate fusiform i n i t i a l s , in a d d i t i o n to increasing the number of fusiform initials, brought about a significant increase in the circumferential area of the cambium. Assuming that the size of the cells in the wood reflects that of the initials in the cambium, the transfor mation of a cell that measures 400 us x 120 um to one that is approximately 60 00 um x 35 um yields an increase in tan gential area of approximately 400S.

The fascicular rays are quantitatively an important com ponent of the wood of A«_ communis, constituting approxi mately 35% of the total tangential area in peripheral reg io n s {Fig® 51) . In th e innermost wood, however, this value is usually significantly lower. As with the tra c h eid s, a pattern of ch an g in g ray cell size is apparent in the wood. In contrast to the tracheids, the ray cells are longest in the first-formed wood and shortest near the periphery. In the inner wood, ray cells are generally tall and narrow, with average heights in excess of 250 um and 3 7 w idths ia the 20-30 um ra a g e (Fig.. 54)® it successively greater radii*? the cells become progressively s h o r t e r and broader, and near the periphery o f th e xylem cylinder mean cell height and w id th are around 110 um and 50 um, resp ec t i v e l y {Fig® 54) • Incorporating the data for ray cell size i n t o Equation Ho® 10 shows the change in number of ray ini tials ia the cambium (Fig® 53)® In general, there is a marked increase in the number of ray initials as the cambi um develops® Analysis of individual rays within the wood suggests that most of the new initials were formed as a result of horizontal subdivision in preexisting ray ini t i a l s (Fig. 55-57) . l e s s important in increasing the num ber o f ra y c e l l s were vertical divisions in the initials

{Fig. 58) „ 98

El ate VII

Arthropitvs c om m uais— Fig. 47—50

Fig® 47® T ra n s v e rs e s e c t io n of fascicular gone sh o ein g pr i ma ry/secondar y xylemtransition® Bote f i l e s of secondary elements originate adjacent to putative metaxylem tracheids (small arrow) and metaxylem parenchyma (largea rro w ). . C® B® 8576 E bot #7® x 110® Fig. 48® Tangential section through, zone of metaxylem® Mote tr a c h e id s w ith scalar If ©rm thick enings on tangential s a i l s and thick-called parenchyma c e l l s w ith horizontal end calls® C.B® 8576 El s id e #15® x 110® Fig 48® Eadial section of interfascicular ray shoeing gradual change in organizatioa from primary to secondary p a rts o f ray® F ig u re i s oriented such that pith is a t l e f t . C.B® 8576 C1 side #11. x 25. Fig® 50. Transverse s e c t i o n through Interfascicular and adjacent fascicular segments. Note files of interfascicular ray c e l l s shooing transition to tracheid files (small arrows). Also note file of tra cheids intercalated between pcexisfing files (large arrow). C.B. 8576 E bot #2. x 50. PLATE V II 100

I ig» 5 1-5? — Developmental Data for flrthropitys communis

51 s Graph of percent composition of tracheid ccmpc- nent and fascicular and interfascicular ray versus percent wood radius. Note reduction in interfascicular segment ( 3 ) and increase in fascicular ray (#) and tracheid (A) a r e a .

52 l Graph of tracheid length and mean width versus percent wood radius., Note steep increase in length in inner wood and more gradual increase in outer wood. Vertical tars on either side of mean width correspond to one standard devia tion., Length (A) I width {®)» TO* I I I -I J U> NJ o o o o l=S=l — I—O H t—@H I— - H b-O I—@—I I—©—1 f—©—I RCED ZE E IZ S TRACHEID O fs) AGNIL RA (%) AREA TANGENTIAL o & o O'

> o a> o o 101 102

Developmental data for Arthrocitvs communis—Fig, 53-54.

5 3 ; Graph of number of fascicular ray cells and tracheids versus percent wood radius. Note t r a c h e i d number in c r e a s e s i n in n e r wood and ra y cell number increases over entire xylem thick n e s s . hay (#); t r a c h e i d (A).

54: Graph of mean fascicular ray cell size versus percent wood radius. Note dramatic reduction in cell length (H) from inner to outer wood and concomitant increase in width{O ) ■ Bars correspond to one standard deviation. FASCICULAR RAY CELL SIZE (MM)

3 . 0 NUMBER OF CELLS ( x 1 0 ? ) o o H* fsJ

-0 1

D? GM (A ^ O

03O B-

o o 1 04

P la t e VIII

Arthropitvs communis — fig., 55-61

Fig® 55-58® Tangential series from inner to outer Hood showing representative tracheid and ray® All s 110® Fig® 55® Section of inner wood showing three-cell-high ray (large arrow) and tip of elongating tracheid (small arras® C«B® 8539 D s id e #121® F ig . 56® S e c tio n showing same r a y as in preceding figure (large arras)® Bote tracheid tip (small arrow) relative to position in Fig® 55® C®B® 8539 D side # 65® Fig® 57® Same ray as in previous figures® Note that middle cell divided .forming ray four-cells high (large arrow)® Also note that tracheid tip has elongated beyond field of view (small arrow)® C® B® 8539 D side #10® fig® 58® Same cay as ia previous three figures® Bote that basal cell divided longitudinally (large arrow)® . G®B® 8539 D s i d e #1® Fig® 5.9-61® T a n g e n tia l s e r i e s showing conversion of interfascicular ray cell to tracheid. All s 120. Fig®, 59® Section o f inner wood showing elongate parenchyma cell (arrow). C.B® 8539 D side #278. Fig® 60. Same cell as pre vious figure. Bote general increase in length of cell. C.B. 8539 D side #258. Fig. 61. Same cell as in previous two figures (arrow). N ote continued increase in length of cell. C.B. 8539 D s id e #257. PLATE VIII 105 106 itgfchsopifcfs felfcoiltes

The histology of the secondary xylem suggests that the caa- biua in Srthropitys deltoides was characterized ty two distract zones corresponding to the fascicular and inter fascicular segments of the wood {Fig- 62)- la the fascicu lar region* the distribution and organization of the prima ry vascular bundles is s i s i l a £ to that ia L, communis. a narros zone o f metaxylem tracheids is located externally to the protoxylem lacunae (Fig® 63* 6 4 )- The Dietary le e zone is bounded laterally cn both sides by elongate thick-nailed parenchyma cells that merge with ground parenchyma in the interfascicular region (Fig. 63* 64). Badial files of sec ondary tracheids abut metaxylem tracheids and parenchyma

(Fig- 63)* suggesting that the last-formed primary cells and the first-formed secondary cells were derived from the same initials. This implies that the fusiform cambial cells originated from the outermost procamtial initials.

Files of interfascicular ray parenchyma cells radiate from the ground parenchyma between th e .xylem bundles (Fig- 63) indicating that the interfascicular cambial initials feere also derived by the conversion of peripheral procamtial cells or their derivatives.

Hood analysis was conducted on a total of three speci mens which ranged in outside diameter from 6-2 to 7.6 mm.

Thickness of the secondary xylem cylinders in the stems was 107

between 2<.4 and 3.3 mm. Data obtained from the study of a

single representative axis are described in this section.

Information pertaining to the other stems is included in

Appendix £.

The distinctive dilitation of the Interfascicular rays in A. deltoides Is reflected in the gradual increase in

the percent composition of this component in serial tangen

tial wood sections (Fig. 69). The interfascicular segment

accounts for approximately 15% of the total tangential area

in the inner secondary xylem and about 25% in the outer

wood. The change is progressive and gradual. The percent composition of the fascicular component decreases from

about 85% of the total tangential area In the inner wood to

70% in the outer wood. The axial system in the fascicular segment is composed entirely of elongate tracheids and

accounts for between 70 and 80% of the total wood area.

The percent composition of the fascicular rays is usually

between 5 and 10% (Fig. 69). In general, there is a gradu

al increase in the parenchymatous component (interfascicu lar and fascicular rays) toward the periphery of the wood

and a concomitant reduction in the percent tracheid area.

Accompanying these changes In general construction of the wood are modifications in the appearance of the component cells. Some of the developmental changes have been described in an earlier publication (Cichan and Taylor, 108

1983)o Additional observations are made in the present analysis* and the patterns of change are evaluated in the contest of cambial development.

As noted above* the interfascicular rays in JU, deltoides broaden conspicuously toward the periphery of the stem. Associa ted aith this increase in tangential width is a change in the shape of the ray cells. In general* the cells become shorter and tangentialiy eider at successively larger radii {Fig. 70). in the inner wood* the cells are usually in excess of 200 urn long* and the width averages about 20 urn. Near the periphery of the woody cylinder mean c e l l l e n g th ra n g e s betw een 120 and 140 urn* and th e av erag e width is approximately 60 unu These changes suggest that* with increasing girth* there were modifications in the shape of the interfascicular cambial initials* and it has been proposed that changes in size alone might have been responsible for the increase in breadth of the interfasci cular ray (Cichan and Taylor* 1983). Analysis of the data utilizing EQ10 indicates that the number of ray initials increased steadily from the inner to the outer wood {Fig.

71). Thus* the apparent change in cell shape and size could not have fully accounted for the broadening of the rays* and multiplicative divisions were necessarily impor tant in the development of the interfascicular segment. 109

la jU deltoides there is a characteristic pattern of

increasing tracheid site froa the inner part, of tie woody

cylinder to the outer part (Fig. 72). In the first-formed

wood, the length of the cells usually ranges between 6 and

7 EEs, and the tangential width averages approximately 60

urn. At successively greater radii, the elements are pro

gressively longer9 and the longest cells are observed la

the peripheral parts of the wood. She change ia length is

progressive and gradual (Fig. 65-68), and maximum tracheid

lengths generally ranged from 12 to 15 mm. Similarly, tan

gential tracheid width increases (Fig® 72), although the

change in size is not as dramatic. In the outer wood, max

imum w id th s u s u a lly ra n g e d betw een 90 and 95 urn. T his p a t

tern of tracheid enlargement in the wood suggests that cam

bial development in A. deltoides was characterized by a

gradual increase in the size of the initials. Assuming

that the tangential area of the wood cells accurately

reflects the size of the cambial initials from which they

were formed, the data can be analyzed using EQ9. As shown

in Fig. 73, the number of fusiform initials in the cambium

remained relatively constant as the meristematic layer

increased in circumference. Shis pattern suggests that the

rate of increase in the size of the fusiform initials was sufficient to accommodate tangential stress brought about

by the centripetal production of tracheids. She constant 110

enlargement of the fracheids, with no evidence of periodic

reduction in cell size indicates that multiplicative divi

sion of the fusiform initials* if present, m s not a sig

nificant phenomenon in the development of the axial compo

nent of the Hoodo

In contrast to the dramatic developmental increase in

tracheid size, the change in the fascicular cay cells is

less noticible, but is nevertheless distinct® In the

innermost wood, ray cells are usually oval in tangential

section with a height-width ratio of about 5®0 s 1. Cell

height averages close to 100 urn* and mean cell aidth is

about 20 urn (Fig® 74). The width of the cells gradually

increases toward the periphery of the stem, and in the out

ermost wood ray cells are usually between 30 and 40 urn aide

(Fig. 74). Cell height decrease centrifugaily,but the

change is more gradual® Ihe last-formed interfascicular

ray cells usually range in height from 55 to 60 um (Fig®

74). Thus, the cells are rounder in appearance than those

of the Inner wood and exhibit a height-width ratio of about

1.6 5 1. analyzing the data using Eguaticn So® 10 shows

that the number of fascicular ray initials Increased rather slowly early In development, indicating a rather low rate

of multiplicative division (Fig. 71). As the girth of the stem became larger, however, this rate Increased dramati cally. Analysis of the radial files in tangential sections 111 suggests that nee initials were formed by both horizontal and lateral (vertical) division of preexisting ray initials

(T ig. 66—68)® 112

P la te XX

Arthrocitvs deltoides—Fig. 62-68

Fig., 62. Transverse section of stem showing fascicular and interfascicular segments. C. B. 209 B1 side #17. x 16. Fig. 63. Transverse section of fascicular zone shoeing dis tribution of cells around protoxylem lacuna. Note file of secondary tracheids originating at presumptive metaxylem tracheid (arrow). C» B. 7290 B top #36. x 110. Fig® 64. Tangential section of primary lylea bundles separated by zone of interfascicular parenchyma (IF). Note protoxyle® lacuna on left and EetaxyXes on right® C.B. 209 B1 side b #33® x 15 0® Fig. 65-68® Tangential series from inner to outer wood shoeing relationship between tracheid tip and representative ray. All s 35. Fig. 65® Section of inner wood shoving tracheid tip (large arrow) and narrow four cell-high ray (small arrow). C.B® 209 B1 side b #20. Fig® 66. Same ray and tracheid as in previous figure. Note extent towhich tracheid has elongated relative to position of ray (small arrow). C.B. 203 E1 side b #18. Fig. 67. Same ray andtracheid as in previous f no figures. Note that tracheid tip (large arrow) has reached level of four-celled ray (small arrow). C.B. 209 B1 side b #17. F ig . 68. Same ray and tracheid as in previous three figures. Note that tracheid tip has exceeded level of ray (largearrow) and that ray has become multiseriate (small arrow). C.B. 209 B1 s i d e b #15. PLATE IX 113 114

Fig- 69-70 — Developmental Data for Arthropity s deltoides

69*. Graph of percent area of tracheid component and fascicular and interfascicular ray versus per cent wood radius. Note increase in parenchyma tous component from inner to outer wood- Tra c h e id (A ); interfascicular ray { H ) ; fascicular ray (®) .

70: Graph cf interfascicular ray cell size versus percent weed radius- Note decrease in length (11) and increase mean (Q) width at progres sively greater radii. Vertical tars correspond to one standard deviation above and below mean. [%) TANGENTIAL AREA INTERFASCICULAR RAY CELL SIZE (MM) O O I o

WOOD RADIUS [%) 1 16

Fig- 7 1-7 2 — Developmental Data for Arthropitys deltoides

71: Graph of number of fascicular and interfascicu lar ray cells versus percent wood radius- Note general increase in both components from inner to outer wood. Inter fascicular ray cells {® ) ; fascicular ray cells (A).

72* Graph of tracheid length and mean width versus percent wood radius,, Note dramatic increase in length from inner to cuter bood- Vertical bars correspond to one standard deviation above and

below mean- Length (A) 3 width (Q)« 117

9 . 0

7 . 0

X Vi 5.0 U A © fe 3.0 A UK ffl Ds Z 1.0

X 20 4 0 6 0 8 0 100 WOOD RADIUS (%)

15.0

12.0

9.0

6.0

= . 10

.0'

20 40 60 80 100 WOOD RADIUS ('/.) 118

F ig . 73-74 — Developmental Data lot Arthropi fcys deltoides

7.3: Graph of number of tracheids versus percent wood radius. Note stable tracheid number at progressively greater radii.

7 4 f Graph of fascicular ray cell size versus per c e n t vcod radius. Note reduction in height (SUM nd increase in w idth (@) from inner to out er wood. Vertical bars correspond to one stan dard deviation above and below mean. TRACIiF. 11) Ml’M ill'I' (CKI.1.51 FASCICULAR RAY CELL SIZE (MM) o>o v0o

OT. OU o o o m (%) (%) smova

|— ©-H-

| ©-+■ oO 119 120 mb m o s t a as

In Medullosa noei, each vascular segment consists of a central core of xylem and parenchyma surrounded by a band of secondary wood (Fig. 75-76). In most stems* the seg ments are not terete in transverse section* but* rather* they tend to be laterally elongate and tangentially flat tened. Delevoryas (1355) suggested that the flattening is not an artifact of preservation and that it represents the natural morphology of the stem in this unusual plant. The secondary xylem forms an irregular* often discontinuous* ring around the periphery of the segment® Relatively large amounts of wood occur along the inside and outside margins* and little* if any* is found laterally (i® e.0 at the tan gential boundary between adjacent vascular segments).

Because the appearance of the wood in cross sections of

Medullosa does not conform to a circle* and because the oragnization of wood around the vascular segment is asymme trical* the eguations used to analyze cambial development in this plant are different from those presented earlier®

Except in large stems* where the secondary xylem is often deeply loied and irregular* the outline of the vascular segment and woody zone in Medullosa conforms to the shape of an ellipse. The circumference of such a figure (Ce) is 121 approximated by tie equation

S a2 + S i*

Cs - 2 i t x

M 2

a here Sa = the long radius of the ellipse* and

Sb = the short radios of the ellipse*,

This analysis focuses exclusively on the development of

95half aood zones*” and thus the circumference utilized Mas that of a single ”half-ellipse”s

Sa2 * Sb2

Ce = 7T x

Thus* the area of the elliptical half-cylinder is defined by:

(17)

Ae = Ce x fl where H* fcy convention* is set equal to unity-

Substituting Ae for the parameter Ac in Equation No» 9 y ie ld s

(18)

F x Ce

L f X Hf

(the symbols F* Lf , and u£ are defined in Equation No. 9). 122

This modified form of Equation No. 9 was used in analyzing cambial development in Medullosa..

The central portion of the vascular segment in Medullo sa is characterized by bundles of sinuous tracheids embed ded in a matrix of ground parenchyma (Fig® 75, 76) * The parenchyma cells are often poorly preserved and many con tain a dense ergastic substance., The tracheid bundles

ap p ear to be o f two types, distinguished on the basis of

the pattern of secondary wall thickening in the cells®

Most of the bundles are composed of elongate tracheids with oval to circular bordered pits (Fig® 77)® Less freguent

are bundles in which the tracheid walls are thickened in a scalariform or helical pattern (Fig® 78)- Because of the extensible nature of the walls, the latter elements presum ably correspond to the primary xylem. In contrast, because they are morphologically similar to the secondary tra cheids, the former probably represent “post—primary" ele ments that formed within the vascular segment after the onset secondary growth (e®g „g Delevcryas, 1 955)® The dis tribution and arrangement of the bundles of primary tra cheids and their relationship to the elements o f th e wood is unclear because they cannot be discerned consistently from the bundles of pitted tracheids in cross section (Fig®

75, 76) - Serial longitudinal sections, however, suggest that at least some of these primary tracheid bundles are 123 located near the vascular segment/secondary xylem boundary.,

Many of the radial.files of secondary elements appear to have originated in close association w ith tracheid bundles

(Fig® 76} suggesting that the two were derived from th e same initials® ether f ile s seem to have formed de novo within the ground parenchyma of th e vascular segm ents and at the level depicted they are not in contact with tracheid bundles (Fig® 76) ® Files of ray cells radiate from ground parenchyma and often exhibit dense amorphous c e llu lar inclusions like those of the cells in the vascular segm ent

(Fig® 76) i n d i c a t i n g a p o s s i b l e common o r i g i n of th e two tissues. It is important to note that these conclusions regarding early cambial development in Medullosa are te n tative since significant structural changes appear to have occurred w ith in the v a s c u la r segment after primary growth had ceased. D etailed analysis of developmentally young axes is required to accurately assess the relationship between primary tissues and those that were formed later in development®

Analysis of the wood was conducted on a total of five specimens in which secondary xylem thickness ranged from 7 to 18 mm. Only the ceatripetally produced portions of the woody cylinder were examined. Graphs of data obtained from the analysis of a single representative specimen are included in these results; information pertaining to the 124 other ’f our stems is presented in tabular form in Appendix

A study of the percent composition of the wood shows that there is marked variability in the different cellular components within the tissue® In the results depicted in

Fig® 79 higher percentages of ray tissue are present in the inner wood than in the outer wood. Other stems that sere examined showed different patterns in the organisation of the wood; in some the percent ray composition was highest in the outer wood® and in others it remained relatively constant throughout® The significance of this variability is not clear® and additional studies are needed to deter mine the basis for these diverse patterns in wood composi t i o n .

The axial system in the wood is composed entirely of elongate® large-diameter tracheids (Fig® 76® 82-84). Anal ysis of the cells at progressively greater radii shows that on the average element length does not change substantially from the inner to the outer wood (Fig. 80). In general® the length of the cells varies from about 15 to 28 mm; these values conform to earlier estimates for EL noei and

H. anglica suggested by Andrews (1940). Analysis of cells in individual files using serial tangential sections shows that the tracheids undergo alternating sequences of elonga tion and subdivision (Fig- 82-84) thus yielding the appar- 125 eat constancy in length» Subdivision of the tracheids rcaa he recognized by the appearance of an elongate obligue cross wall (Fig- 83). At progressively greater radial dis tances from the point at which subdivision occurred? the length of two newly formed cells increases. Within a spec imen? the tangential width of the tracheids remains rela tively constant or increases slightly towrd the periphery

(Fig. 80). Ihe change ia size? when present? is gradual.

Tracheid diameter ranged from approximately 125 to 150 urn.

Study of the ray system in Medullosa is made difficult by the inconsistent preservation of the cells? especially in the interior of the rays. When present? ray cells ia this inner region often appear smaller and thinner-walled than those that are contiguous to the tracheids. The inability to examine sufficiently large numbers of cells from different radii prohibits a guantitafive analysis of the ray system.

In a single specimen? cellular continuity was observed between the wood and the phloem {Fig. 85). In this stem? a one- to two-cell wide band of thin-walled cells appears to represent the cambial zone ; cell files are continuous across the region from the secondary xylem to the phloem.

Cells which appear to represent fusiform initials are elon gate and radially narrower than the tracheids (Fig. 85?

8 6 ). In contrast? the tangential diameter of the cells is 126 equal to* or slightly less than* th a t of the tracheids.

The absence of sieve areas on the Halls of these cells*

(e .g .* Snoot* 1984) suggests t h a t th e y are not s ie v e ele ments. Furthermore* it is unlikely that the elements rep r e s e n t remnants of the last-formed c am b ial Initials ia a determinate lateral m eristem since determinate growth i s unknown in fled u l l o s a . Because the tangential area of the tracheids appears to approximate that of the fusifcsa in i t i a l s from which they were derived* the data for tracheid size can be incorporat ed into Equation No. 25 to provide an estimate for the num b e r of initials in the cambium at each radius examined. A graph of the data shows that the number of fusiform ini tials increased steadily as derivatives were produced centripetally (Fig. 81). The sharp increase in number is pre sumably associated with "simultaneous" anticlinal divisions in neighboring initials. Based on an analysis of the change in the number of fusiform initials versus the actual radius (in contrast to the percent wood radius)* it was determined that new initials were added to the cambium at a r a t e o f approximately 0.64 cells per mm of xylem accretion.

The quantitative data are thus consistent with qualitative interpretations* and periodic multiplicative division of the fusiform initials appears to have been present in the cambium of Medullosa. 127

P l a t e I

Medullosa— fig. 75-78

F ig . 75. Transverse section of vascular segm ent and ad ja c e n t secondary xylem. Hofce numerous tracheid bundles in ground tissue of segment. C.B. 831 B4 top #7. x 20. Fig. 76. Transverse section of primary/secondary xylem i n t e r f a c e showing tracheid file originating in ground parenchma of vascular segment (small arrow) and in association with tra cheid bundle (large arrow). C.£. 831 E4 to p #7. x 11.5. Pig. 77. Tangential section of vascular segment showing bundle of pitted tracheids. C.E= 1239 B side #15. x 35. Pig. 78. Tangential section of vascular segment showing tracheid bundle of elements with scalarifors thickenings. C.B. 1239 B side #16. x 35. PLATE X 128

v < h •v>. ' J u P ^sy\ jS\ iv**t > .* ■+-* ..>w' ' , 1 1 " v w > j, %/.■/ ) s ;ir ~— • V '*r > ; v 'y s ^ '•■'~ ~-'fh;V v A A : ? '- - * H '■#**’• ■' ’ I k h f. :(f s \ f. ■“ - *f> ^8 . r > ~— - i 4 • ...... / '.-.>**;cV > n,31 % ;- J f \ r- S ■ •' ■ ••'>'' ^ * . ✓ i T Vv 'C? - . « . k w fl ' • - M V *• ,( * V- W * * »* * • ' * * > t* * ^ v - f

f ’ - ■ ...

& « “ es . , \ «

; ■» ■ *

< 4 1

. "Z-r.C;-ti •• •*• '- ■ y * v,::V \ \ Vf I f I » .,/'** f %< » ' , y ? & . ‘ a \ . \ t • I '• i • "" . €9 ... * \ \ \ \-. (; j ' \. f ., * •' * r : & G Srf‘ * >*\ \ \ \ \ ji \ \ ' .»o' - *■* ■ v - 55 • - . ■ y * :" '

■> , • V

F ig- 79-8C — Developmental Data for Medullosa

7 9 : Graph of percent composition versus percent wood radius- Note irregular pattern in wood composition- Ray percentage { # ) is high in inner wood and tracheid percentage (A) i s high in outer wood-

80: Graph of tracheid length and mean width versus percent wood radius- Note relatively constant length (A) and mean width (®) from inner to outer wood- Vertical bars correspond to one standard deviation above and below mean- TRACHEID SIZE (MM) «®, TANGENTIAL AREA (/.) o PO O' CD o o o o o o o

M o o

& o

& © ffl * o

© p

& A p p

m p

u o 131

10.0

B.O

^ - wu 6.0 © © wce D z o 4.0 u u

2.0

20 40 60 80 100 WOOD R A D IU S {%) © °

F ig. 01 — Developmentar Data foe Medullosa

Graph of number of tracheids versus percent wood radius® Note gradual Increase in number of cells at progress!vely greater radii® 132

P late XI

Kedaallosa-—Fig® 82-86

Fig® 82-84., Tangential series of intermediate wood showing ev id en ce of anticlinal division of fusiform initials and fusiform initial elongation® All x 20® Fig® 82® ’Se c tio n showing tr a c h e id tip {arrow) and tr a c h e id {X)® C-B® 831 B4 s id e b #12® Fig- 83® Same iracheids as in previous f ig u r e - Note tracheid tip has elongated beyond original position in Fig® 82 and a new tracheid (X1) has appeared adjacent to tracheid X® C-B- 831 B4 s id e b #10® f i g - 84- Same tracheid as ia previous two figures- Mote that tracheid tip has continued to elongate farrow) C„£® 831 B4 #8- Fig® 85- Transverse section of outer wood and adjacent extrasjlary tissues- Arrows indicate presumptive fusiform initials- C-B® 831 B4 top #3- s 70- Fig® 86- S l i g h t l y o b lig u e ta n ” g e n t ia l section of extraxylary zone showing p u t a t i v e cam bi- a l zone (CZ) - C. B. 831 B4 side a #3. x 60- PLATE XI 133 134

COBDUTAlgS

Primary xylem in cordaitean stems (Fig® 87) is composed of tracheids with annular* helical and sealariform secondary wall thickenings and abundant xylem parenchyma arranged in longitudinal strands (Pig® 88* 89)® 2he shape of the par enchyma cells resembles that of cells from the outermost portions of the pith® Cross sections reveal that the cells are organized into distinct radial files (Fig® 87)® Gradu ally* the files of primary xylem merge with those of the secondary xylem (Fig. 87* 89) * and there is a morphological change in the wood from elements with extensible thicken ings to those with circular bordered pitting on the radial walls (Fig. 89). The gradual radial transformation from primary to secondary wood is also evident in the reduction of the parenchymatous component in the tissue (Fig- 93).

Thus* no distinct interruption occurs between the two xylem types suggesting that they were both formed by the same initials. Conseguently* it is likely that the cambial ini tials in the fascicular zones of cordaitean stems were derived directly from cells of the procambium®

Wood analysis in the cordaites was conducted on a total of five specimens that ranged in outside diameter from 5-0 to 34.0 ii. Thickness of the secondary xylem cylinder in the stems ranged from 2.1 to 18.0 mm. Graphs obtained from the analysis of a single representative specimen are illus 135 trated la this section® Information pertaining to the oth er four specimens is presented in tabular form in Appendix

The percent composition of the tracheids and the rajs in cordaite mood is relatively stable (Fig® 93)® The raj com ponent comprises between 5% and %0t of the total mood area in tangential sections, and the tracheids account for the remaining 90 - 951® .Four of the stems examined conform to the genus Cordaixfloa sensu Grand®Eury (Rothwell, personal communication), and tie fifth specimen, which is described in this section, was identified as Hesoxylon (Scott and flaslin, 1910). It was observed that in the former, the percent ray area in the wood was consistently lower than that in the latter. In general, rays in Cordaiavion accounted for 2 to 5% of the tangential wood area. These quantitative data, although preliminary, confirm Bothaell*s

(personal communication) suggestion that wood composition can. In part, be used to distinguish Mesoxylcn from Cor- d a ix y l on.

Analysis of tracheid length in cordaitean wood shows that cells in the first-formed secondary xylem are rela tively short, usually averaging less than 3 mm in length

(Fig® 94). At progressively greater radii, cell length in c r e a s e s g r a d u a lly and a t t a i n s a maximum mean v alu e of between 4 and 5 mm at intermediate radii in the wood. From 136 this point outward, cell length remains relalively stable with only minor fluctuations. The pattern of change in the tangential width of the tracheids is similar to that observed for tracheid length. The cells are narrowest in the inner wood where average widths are about 30 ua (Fig.

94). The cells gradually become wider at successively greater radii and attain a Maximum mean width of .between 35 and 40 um in intermediate portions of the wood. Beyond this pointy tangential cell width does not change dramati cally and usually remains relatively stable to the periph ery wood (Fig® 94). Assuming that the length and width of the tracheids does not change significantly during differ entiation of the woods the data can be incorporated info

Equation Bo. 9 to yield information about changes in the number of fusiform in itials during cambial development. As

Fig. 95 indicates, the cambium that formed the inner wood generally contained fewer fusiform initials than that which produced the outer wood. The change in number is progres sive and gradual and occurred at a rate of about 33 cells per mm of xylem accretion. Analysis of individual files of cells in serial tangential sections indicates that the increase was brought about by anticlinal division of preex isting initials. As far as can be inferpretted from the wood, th e p r o c e s s was c h a r a c t e r i z e d by th e p ro d u c tio n of a cross wall with a pseudotransverse orientation in the moth 137 er initial* thus forming two daughter cells (Fig® 91 * 92)®

The two initials that were produced were significantly shorter than the mother i n i t i a l * and a s development pro g re s se d th ey e lo n g a te d intrusively® Thus* the apparent stability in tracheid length in th e outer parts of the wood i s a reflection of the alternating sequences of reduction and subsequent elongation®

The s i z e of the ray cells increases from the in n e r to th e o u t e r wood (Fig® 9 6 )® l a the first-formed secondary xylem* cell length averages between 35 and 40 urn* and cell width ranges between 20 and 25 urn® The ch an g e in cell size i s gradual* and in the ou ter wood* the c e l l s are between 45 and 50 urn long and exhibit widths of about 30 urn. Analysis of these data u t i l i z i n g Equation No® 10 shows that there was a r e l a t i v e l y high number o f ray i n i t i a l s in the cambium th a t formed th e e a rly wood (Fig® 97). This presumably reflects the distinct parenchymatous character of the pri mary xylem® At progressively greater radii, the number of c e l l s d e c re a se d dramatically* and following t h i s th e r e was a marked in c r e a s e in th e number o f ray in it ia ls ® 138

S la te XII

Cordaitean Stem s-- I i ^ _ 8 7 r 92

Fig® 87- Transverse section of primary/secondary x y le a transition zone- Note large radial diameter o f prim ary tr a c h e id s and their distinctive radial alignment- C.B» 930 C to p # 10- x 110- Fig- 88- Tangential section of primary xylem showing tracheids with helical/scalarifora secondary thickenings. Note abundance of ray-like parenchyma- C.B. 1014 D side a #28- x 130-, Fig- 83- Badial section of primary/secondary xylem transition zone showing gradual progression from helical to scalarifora to scalariform pit ted to oval* bordered pitted elements- Note radially arranged parenchyma at'top- C. B. 101*} s i d e t #1- x 130- Fig- 90- Tangential section of inner wood showing well- developed ray component. C. B. 1014 d side a #26® x 110- Fig- 91-92. Tangential series showing evidence of anticli nal division of fusiform initial. All x 130. Fig- 91- Sec tion showing tracheid (X) . C .B . 930 C side #28. Fig. 92- S e c tio n showing same tracheid as in previous figure. Note o b liq u e partition at arrow indicating t h a t cam bial i n i t i a l had divided. C.B. 930 C s i d e # 19® PLATE X II 139 140

Fig, 93-94 — Developmental Data for Cordaite Stems

93:’ Graph of percent area of tracheid and ray com ponents versus percent wood radius. Note rela tive stability of both components throughout wood., T rac h e id (A); cay { # ) .

94: Graph of tr a c h e id le n g th and mean w idth v e rsu s percent wood radius. Note increase in length (US) and width (#) from inner to outer wood, Vertical bars correspond to one standard devia tion above and below mean. TANGENTIAL AREA {%) TRACHEID SIZE (MM) 100 OD AIS (5S) RADIUSWOOD

eia&

o U 2

Fig. S5-96 — DoveIopmental Data for Cordaite Stews

95: Graph of number of tracheids versus percent wood r a d iu s . Note g e n e r a l in c r e a s e in number of cells at progressively greater radii.,

g6*. Graph of mean ray cell size versus percent wood radius- Note general increase in both length (H) and width {©) from inner to outer wood- Vertical tars correspond to one standard devia tion above and below mean-

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Fiy- 97 — Developmental Data for Cordaite Stems

Graph of number of ray cells versus percent wood radius. Note slight reduction in inner most wood and g ra d u a l in c r e a s e in numfcer tow ard p e r ip h e r y - 145

Figure 98: Cambial Development in Terete versus Elliptical Axes. Increase in radius has greater effect on circumference of terete figure compared to elliptical one. See text for explanation. Cfeafter 21 DISClSSlOH

IgglBOPlHDBILBS

h nalysis of cambial development in the arborescent lycopods

is based ' on the assumption that the organization of the

wood directly reflects the histologic organization of the

cambium at the time the derivative tissue was formed. More specifically* it supposes that any changes that might have

occurred in cell size and shape during differentiation and

maturation were minor. This hypothesis appears to be

severely tested when examining the extremely large tra

cheids in the wood of this group* and thus it is valuable

to examine the evidence on which the assumption is founded

and to evaluate other interpretations of the data.

In the classic study by Bailey (1920)* and in a subse

quent investigation by Bannan (1965)* it was observed that

the length of secondary conducting elements differed little

from that of the cambial initials from which they were

formed. During the transition from fusiform initials to

tracheids in conifers* the cells elongate by less than 10

percent. Similarly* in Abies Wilson (1963) observed a

- 147 - maximum increase in length of about 13 percent during dif ferentiation, but mean values Mere much loser. In angiosperms, changes in vessel element length during differentia tion are even less significant (Bailey, 192 0), vith virtu ally no change occuring during the progression from in itial to mature cell*. In contrast, ho sever, cell length increas es markedly during development in wood cells that function principally in support (e.g., libriform fibers and fiber tracheids), and at maturity these elements are much longer than the initials from which they were formed (Chattavay,

1936)« Although wood composition in the arborescent lyco pods is like that of gymnosperms, being homogeneously com posed of tracheids and rays, a functional dichotomy similar to that observed in the angiosperms appears to have teen present. It has been suggested that the thick, presumably sclerified periderm uas responsible for providing mechani cal stability to the axis and that the secondary xylem sas principally involved in conduction (Walton, 1953; Carl- guist, 1975)» Based on their apparently important role as conductive elements, it is reasonable to suspect that the length of the secondary tracheids in lepidodendrid axes increased little, if at all, during differentiation and maturation.

The present analysis of lepidodendrid wood indicates that the change from short to long cells was progressive and continuous within an individual file* That is* each tracheid is slightly longer than the one that precedes it in the radial rot*. This generalization obviously excludes the aaaomalous and presumably random phenomenon o£ cellular subdivision and reorganization present in the aood» To explain the pattern of change in cell lengthy it was pro posed that the meristematic cells responsible for forming each .file increased in length after each periclinal divi sion* Similar patterns in extant plants have also been regarded as evidence of a gradual change in size of fusi form in itials (Bailey* 1923* Bannan, 1962; Carlguist* 1962;

Cumbie, 1S69a; Ghouse and Hashmi* 1981; Khan* Siddigi* and

Khan* 1983). An alternate explanation for the phenomenon is that the fusiform initials maintained a constant length* and each centripetally produced derivative was sequentially conferred with an increased potential for elongation* In cambia where the the length of the fusiform initials remains relatively constant* however* a pattern of increas ing tracheid length is not evident in the wood (Bailey*

1920; Butterfield* 1972; Carlguist* 1975)* Moreover* in such cases the secondary xylem of ten exhibits a storied appearance (Philipson et al* 1971)« Since there is no evi dence of such organization in the wood* and the pattern of tracheid length increase is well defined* it is likely that the length of the fusiform initials increased as cambial development proceeded* la coniferous wood, -the tangential width of the fusiform iaitials and the derived tracheids is virtually identical

(Bilson, 1963; Bannan, 1965). In contrast, because of div ergent structure/function relationships in the derivative xylem cells, development of vessel-contaiming woods in angiosperms is more complex. The tangential diameter of ves sel elements may be more than *400 times that of the fusi form initials from which they were formed (Zasada and

Zahner, 1969). Such a massive increase in size during development is accommodated in the surrounding tissue by the displacement of cells. Adjacent differentiating ele ments apparently maintain sufficient turgor to withstand tangential compression, and none of the surrounding cells are obliterated (Zasada and Zahner, 1969). Since the axial system in lepidodendrid wood is composed exclusively of tracheids, xylem development in this group was probably more similar to that in conifers than angiosperms. This morphological homogeneity suggests that all the tracheids in the wood of arborescent lycopods differentiated in a common m anner, as in modern v e s s e l l e s s woody p l a n t s .

Finally, if the fusiform initals were significantly smaller than the tracheids, then the area occupied by fusi form initials at any given radius in the cambium would have been l e s s th a n t h a t o f th e t r a c h e i d s in th e m ature wood.

In this regard, the total area of the ray initials would 151

have bean greater than in the mature wood. As xylem dif

ferentiation proceeded at that specific radius* the area of the ray component would gradually have become reduced so as to ultimately match the composition in the mature wood®

Such a change would have to have been effected by a reduc tion in the size and/or number of the developing ray cells® hm increase ia tracheid area can occur only at the expense of ray area since the total circumferential area at a given radius is fixed® As far as wood differentiation has been studied in extant plants* there is no evidence that such a process occurs® Seduction in cell size and loss of ini tials are changes that occur exclusively within the cambium and are not known to take place during the differentiation o f th e se c o n d a ry xylem (Bannan* 1950* 1951 ; E v ert* 1961s

Srivastava* 1963; Cumbie* 1967)® Thus* in the wood of arborescent lycopods* there is compelling evidence to indi cate that the tangential width and length of the tracheids

was similar to that of the fusiform initials that produced them and that significant changes in structural organiza tion did not occur during differentiation of the wood®

The data suggest that the increasing girth of the cambi um in arborescent lycopods was accommodated primarily by the progressive enlargement of the fusiform initials. Dur ing the development of the inner wood* there was a sharp reduct ion iri the number of fusiform initials in the cambi- urn. This was followed by a protracted period of lateral growth during which the number of fusiform initials remained relatively constant. Enlargement of the fusiform initials occurred in both the tangential and arial dimen sion; the latter appears to have occurred by intrusive cell growth*. In transverse sections, radial files that appear to originate d@ novo within the wood actually represent the more peripheral portions of files in which the length of the cells increases centrifugally (e.g.„ Cichan and Tay lor, 1S82). In view of the poor preservation of the ray cells, no definitive statements can be made regarding the role of ray initials in the process of cambial enlargement.

In both Paralvcopodites and Stiqmaria the ray system con stitutes a relatively small portion of the total wood area, and thus the effects of changes in this component on the meristem were probably minor. It is worthy to note, how ever, that the developmental constancy of the percent ray compositon of the wood and the apparent stability in ray cell size suggest that some form of multiplicative increase was opperative in maintaining this component.

Is with the secondary ray system, the role of the root let trace rays (BT rays) in cambial enlargement in Stiqma ria can not be assessed because of the poor preservation of the cells. The best-preserved HT rays are generally found in the innermost wood (Fig. 20; see also Frankenberg and 153

Eggert* 1969* Fig® 61)® at progressively larger radii and

as the sire of the HI rays increases* the fidelity of cel

lular preservation decreases (e-g.* Fig®.21)® This nay be

interpretted as indicating a decrease in cell vail thick

ness* perhaps associated with an increase in their size®

In this respect* iilliaason (1889) and Frankenberg and

Eggert (1969) suggested that the large lacunae of the HI?

rays Mere characterized by delicate parenchyma cells that

were obliterated during the fossilizafeion of the axis® la

a developmental contest* the broadening of the RT rays in

Stigmaria may have resulted from the gradual increase in

the size of the cambial initials associated with the ray®

As the ce11s increased in size their derivatives may have

become more fragile and thus* were not preserved to the

extent of other cells in the axis. An alternate explana

tion is that poor cellular preservation in the BT ra y s does

not represent an artifact* but rather that it represents

the actual condition of the rays at the time of fossiliza-

tion® The principal physical stress in an a sis that is

increasing in radius is a tensional force in the tangential

plane (Hejnowicz* 1980)® In an axis unable to accommodate

this stress* tissue disruption will presumably occur along longitudinally oriented lines of weakness® It is thus pro

posed that the lacunae in the R2 rays may have been formed as a result of the schizogenous disruption of the thin- 154 called cambial initials that formed the parenchymatous aspect of the rays® In this developmental scheme* the increasing size of the RT rays did not actively bring about circumferential enlargement of the cambium. Rather* the change in BT ray size is the passive result of the inabili ty of the initials in these isolated regions of the cambium to keep pace with circumferential expansion.

Xylem analysis reveals that nei# fusiform initials in the cambium of the arborescent lyccpods were not produced sys tematically by anticlinal divisions. Instead* new initials seem to have originated sporadically by the partitioning of fusiform initials to form numerous small meristematic cells. Most of the initials that were produced in this manner were subsequently eliminated from the cambium* but some were retained and were ultimately transformed into new fusiform initials. In general* more than one new file of cells seems to have resulted from each localized subdivi sion* and thus the phenomenon is technically a multiplica tive process. The sporadic occurrence of these distinctive regions in the wood and their general absence in smaller axes suggests that they were not intimately related to increasing cambial circumference. In fact* since cambial enlargement appears to have been realized almost exclusive ly through an increase in the size of the initials* such cellular subdivision might have been entirely incidental. 155

Previous workers have regarded the regions as zones of

"imperfect wood" (Silliamson, 1889) and "interrupted wood"

(Frankenberg and Eggert, 1969), and have suggested that they were formed in response to some esternal disruptive factor (e.g.? drought, wounding, or disease). The limited tangential and axial extent of the zones, and the extremely deep-seated nature of the cambium in the lepidodendrids seems to indicate a more "site specific" cause*, The mecha nism by which cambial circumference increased in these plants dictated a minimum rate of cell growth in the ini tials. Ihis rate was intimately related to the rate at which derivatives were produced centripetaily and the extent to which radial enlargement occurred in the differ entiating tracheids. Isolated zones of subdivision may represent sites at which the cellular growth rate was una ble to keep pace with the rate of circumferential enlarge ment in the cambium.

The process of cambial dedifferentiation, whereby the camhial initials gradually changed to unspecialized par enchyma, occurred in both the aerial and subterranian parts of the plant. Presumably in response to an interruption in the supply of biochemical factors required for normal development, the fusiform cambial cells subdivided to form an abundance of snail initials- These cells apparently continued to divide periclinally for a relatively brief 156 period producing derivatives that differentiated into stunted* tracheid—like cells* iith subsequent irregular partitioning of the initials* radial alignment of the cells became less distinct* and the derivatives differentiated into cells with a more parenchimatous appearance* Ulti mately the initials lost the ability to divide and likewise assumed the morphology of parenchyma cells* Thus* struc tural evidence suggests that the cylinder of tissue immedi ately adjacent to the secondary xylem represents a 6)post- meiistematic sheath" (sensu Eggert and Gaunt* 1973). This interpretation differs from that proposed by Eggert and

Kanemoto (1977)* who suggested that the tissue directly contiguous to the wood in Lecidodendron was a primary par enchyma sheath. It should be noted* however* that the hisology of the tissue was not described in great detail by these workers* and different conclusions may result from a reexamination of the specimens using closely spaced serial tangential sections* Furthermore* it is possible that the vascular cambium in the lepidodendrids dedifferentiate according to a variety of patterns depending on* for exam ple* the size and/or age of the axis* the conditions in which the plant grew* and perhaps even the climate at the time that growth ceased,

The results of the present investigation confirm earlier suggestions that the cambium in the arborescent lycopods 157 was u n i f a c i a l {Eggert and Kanemoto, 1977; Arnolds 1960)®

There is no e v id e n c e to indicate that an y cambial d e rin a t i v e s were produced centrifugaily. Thus, the cambium appears to have been developmental!y similar to that in the extant fern Botrichium. the only living vascular cryptogam that produces true secondary xylem {Stevenson, 1980J. T h is excludes th e so-called prismatic tissue in Isoetes which does not appear to perform a conductive function (Paolillo, 1963)

It is noteworthy that, on the basis of theoretical con straints, the plausibility of a true unifacial cambium

(i.e., one which solely produces cells centripetally) has been questioned (Sanio, 1873; Newman, 1956). In this respect, it has been suggested that every periclinal divi sion of the cambial initial was accompanied by the forma tion of a complete primary wall around each resulting daughter cell (Mahmood, 1968; Murmanis, 1970, 1977, although see Catesson and Boland, 1981) If such were the case, then continued centripetal production of derivatives would result in the gradual thickening of the outer tangen t i a l wall o f the cambial initial, and in extremely la r g e axes the wall would become so thick as to interfere with normal cell function. The results of future research on the mechanics of cell division in the cambium will no doubt provide new insights into the patterns and processes involved in the development of the unifacial cambium. 153 sgasii3gagii.ai.Rs

The interfascicular wood of Sphenophvllum has teen an enigma since it was first critically examined by Renault

{1873) g Williamson (1874) * and Williamson and Scott (1894).

These early studies* as well as more recent works (e.g.*

Baxter* 1948; Darrah* 1968; Schabilion* 1969 )g have interpretted the rays in this zone as being composed of distinct vertically aligned cells and horizontally directed cells.

Eggert and Gaunt (1973)* on the other hand* have suggested that a true ray system was lacking in various parts of the secondary xylem because of the apparent discontinuity between vertical and horizontal in Sphenophvllum compo nents. A more recent interpretation* however* suggests that the horizontal and axial components actually represent parts of the same cellular system (Ha* 1977). It was sug gested* however* that the cells were not produced by con ventional ray initials* but rather that they developed from

"axial parenchyma initials." The present study shows that the horizontal parenchyma component in the secondary xylem represents a radial outgrowth of the upright ray cells that presumably formed during wood differentiation. The out growth appears to have developed in conjunction with the radial enlargement of the tracheids and extends from one upright ray cell between circumferentially adjacent tra cheids to the next ray cell. Thus* despite appearances* 159 radial continuity between cells is maintained, and cay files axe present.

On the basis of this interpretation of good structure, it is concluded that the cambium in Sphenophvllum consist ed of isolated fusiform initials that alternated with elon gate bands of upright ray initials one or two cells Hide.

1 sim ilar conclusion was reached by Eggert and Gaunt (1973) based on a study of the arrangement of extraxylary tissues.

In accordance with the dimorphic appearance of the ray cells (i.e., upright cells vs. upright cells with radial outgrowths), a different arrangement of cambial initials might have been present. The ray initials may have teen short and narrow conforming to the radial "peg-like” compo nent of the ray system, and thus, the cambium would have been composed of broad fusiform initials and low ray ini tials longitudinally isolated from one another or grouped in small clusters. During development, the differentiating ray cells might have elongated radially and axially into the longitudinal gaps between enlarging tracheids in con centric rings. Further enlargement of the gap might have been accompanied by the orderly production of cells fro® the tangential face of the longitudinally oriented portion of the ray cell, thus filling the axial intercellular space with clusters of upright cells. The principal evidence against this interpretation is the relationship between the horizontal and upright portions of the cells,. In the scen ario described above© radial elongation of the cells during development aould be almost exclusively centrifugal© since xylem expansion presumably occurred In that direction®

Thus© the axially oriented portion of the cell Mould be closer in proximity to the periphery of the axis than the horizontal portion® That is© in most cases the horizontal com ponent Mould be directed toward the center of the stem®

Is noted earlier© most of the "t-shaped” cells are charac terized by horizontal outgrowths that are directed toHard the periphery of the stem© suggesting that this alternate developmental scheme is probably incorrect® Clearly© definitive statements about cambial structure in Spheno- phvllua are contingent upon the discovery and analysis of veil-preserved axes exhibiting intact vascular cambia. In the absence of such specimens© however© in-depth analysis of wood structure can provide at least tentative answers to guestions related to cambial organization in this plant.

The present study suggests that the increasing size of the fusifcr© initials© as estimated by analysis of the mature derivative cells© was sufficient to account for the tangential broadening of the interfascicular vascular cam bium. In agreement with earlier suggestions (Cichan and

Initials* In cross sections of tie wood* radial files of tr a c h e id s that appear to originate at intermediate p o s i tions within the wood and have been interpretted a s e v i dence for anticlinal divisions in the cambium* (Schabilion*

1969; Ma* 1977 )g actually represent the peripheral portions of files in which the tracheids become progressively longer ceatripefally (Cichai and Taylor* 1982) ; the shorter inner cells in the files are below the plane of section*. Since this analysis focused exclusively on the interfascicular component of the wood* conclusions about cambial structure and development pertain only to that zone* Statements about the formation of the fascicular wood and how the two cambial zones interacted to bring about enlargement of the merisfem will require additional analysis*

Apical and lateral growth in Schenophvllum has been regarded a s d eterm in a te (Eygert and Gaunt* 1973)* The results obtained in the present study of cambial structure and development provide further evidence fo r this conclu sion* Since cambial enlargement was contingent upon the growth of the fusiform initials* ultimate stem girth was li m i t e d by the maximum size that could be attained by these cells* Studies of extant plants indicate that spindle- shaped cells c a n attain lengths in excess of several c e n t i meters (Aldaba* 1927; Esau* 1 94 3 ). Fusiform initials in

Sphenophyllumfl however* had to retain the capacity to 162 divide in an ordered manner® and this fact no doubt se v e r e l y limited the mariaa© length that the cells could a t t a in .

Thus® in Gambia in uhich the change in girth is accommodat ed by an increase in the length and a id th of the initials® th e maximum size the plant can attain is probably limited.

IQ 0 1 5 1 2 1 1 ,1 5

In contrast to Sphenophy11urn® nhere wood anatomy does not directly reflect the organization of the cambium® in

Arthropitvs there is little evidence to indicate that sig n i f i c a n t changes occurred In the s iz e and form o f th e c e l l s d u rin g uocd differentiation. The rationale used in a r r i v in g at this conclusion parallels that used in a n a l y s i s of the arborescent lycopcds. In b o th A. communis and A. d e lt o id e s t h e a x ia l system of the wood is composed exclu s i v e l y of tracheids. In the former® th e s e e le m e n ts appar ently functioned in conduction and in providing mechanical stren g th ® as in th e tr a c h e id s of modern conifers. In A. deltoides which presumably exhibited a procumbent or lean ing habit of growth {Cichan and Taylor® 1983)® th e t r a cheids appear to have been important principally in conduc tion. Studies of modern plants have suggested that the length of secondary vascular elements changes little® if at all® during differentiation {Bailey® 1920; 195 3® 1958).

Thus® it is reasonable to conclude t h a t in Arthropitys the 163 length of the se c o n d a ry tracheids approximates that of the fusiform initials from which they were form ed,

Farther support for the contention that cell arrangement in the wood corresponds to that of the cambium is that there is no evidence of alterations in the ray system caused by tangential enlargement of the tracheids. In the aood of vessel-containing angiosperms, the radial course of ray files is usually deflected because of an increase in tangential width of the developing vessel elements, The extent to which the rad ia l alignment of the f il e s is dis rupted i s related to the extent to u h ic h the conducting cells enlarge during development. The absence of such structural modification in th e fascicular ray system of ftrthropitvs indicates that the changes in tangential t r a - cheid width during differentiation were insignificant.

There is similar evidence to suggest that the size and form of th e ray cells corresponded closely to that of the initials from which they were derived. New ray initials appear to have been produced by horizontal and vertical subdivision in prexisfciag initials. The individual cells are arranged in radial files suggesting that cell division was localized in the cambial zone and not in the zone of differentiation. Subdivision in the zone of differentia tion would be suggested if cay files were extremely limited in radial extent, or if there were sporadic changes in the 164 composition of the rays such that the cells present in one tangential section Mere absent in the succeeding section.

The general absence of both of these structural patterns in the wood of Arthropitvs suggest that changes in the ray component during differentiation* if present* were minor.

In accordance with the recognition of JU communis and

A. d e l t o i d e s a s s e p a r a t e fcaxa* th e wood o f th e two s p e c ie s

Is structurally distinct. In addition to the obvious dif ferences In the appearance of the interfascicular segment* the two can also be distinguished from one another by dif ferences in the fascicular rays* tracheid diameter* and intervascular pitting (Cichan and Taylor* 1983). Perhaps more fundamental* however* are the differences in the pat terns of wood development in the two species. The data suggest that tne increase in cambial girth in JU communis was accommodated by both the increasing size of the fusi form initials and the conversion of cells from the inter fascicular region to fusiform initials. In contrast* cir cumferential enlargement of the cambium in A». deltoides was apparently accommodated by the increasing size of the fusiform initials and by an increase in the size and jiumter of the interfascicular ray initials. In both stems* the gradual increase in size of the fascicular ray system toward the periphery of the wood suggests that this compo nent also played an important cole in dissipating tensional 165 stress in the cambium. I here is no evidence to indicate that the girth of the cambium increased ty anticlinal divi sion of fusiform initials as if does in seed plants. In cross section* radial files that appear to originate at intermediate positions in the wood actually represent parts of files in which the shorter tracheids toward the inside of the axis are below the plane of section. 2his is iden tical to the pattern described in an earlier work dealing with secondary growth in Schenophvllum ’(Cichan and Taylor*

1982).

The nature of these developmental systems lends support to suggestions that secondary growth in calamite axes was determinate (Eggert* 1962j iilson and Eggert* 1974). In

A. deltoides* as in Sphenophyllam, circumferential growth of the cambium was limited by the maximum size that the spindle-shaped fusiform initials could attain. Continued lateral growth in stems of this type would presumably he accompanied by an increase in the parenchyma component in the wood. Such modifications would necessarily bring about a change in the mechanical and conductive capabilities of the xylem and presumably weaken the axis. In communis maximum cambial girth was apparently limited primarily ty the number of interfascicular ray initials that could be converted to fusiform initials. There is no evidence to indicate that fascicular ray initials could be modified to 166 form fusiform initials* and* once the MsupplyM of lateral interfascicular ray initials was exhausted* there would have been little change in the number of fusiform initials®

Consequently* although a mechanism was present to increase the number of fusiform initials in calaaite stems* the max imum girth that could be attained by the cambium was lim it ed* and it is likely that cambial developement aas determi nate®

flED0S.LQSfll.E5

The discovery of a specimen exhibiting a well-preserved vascular cambium provides the basis for a more precise analysis of cambial development in the medullosans® The similarity in the tangential width of the fusiform initials and tracheids indicates that little change occurred in this parameter during wood differentiation® The limited radial size of the cambial zone and its inconsistent longitudinal preservation* however* prevent an accurate measurement of fusiform initial length® Consequently* as in the analysis of previous taxa* both tracheid and fusiform initial length are assumed to have been similar based on indirect evi dence® In modern plants* libriform fibers and other secon dary elements that provide mechanical support in the axis are often much longer than the cambial initals that pro duced them (Chattaway* 1936). In contrast* the length of 167 cells primarily involved in conduction does not change sig nificantly during differentiation* The extreme radial and tangential width of the tracheids in Hedullosa^ their great lengthy and their thin* extensively pitted walls all indicate that these cells had a specialized role in conduc tion® and it is likely® therefore® that the tracheids did not increase in length significantly during wood development. Additional evidence for this conclusion is the fact that, within a file® the increase in tracheid length is gradual and progressive® and reductions in length occur only in association with multiplicative divisions* la mod ern groups this developmental pattern has been shown to be a reflection of changes in the size of the fusiform ini tials rather than cellular modifications that occur during differentiation (Bailey® 1923 ; Carlguist® 1962).

On the basis of the results of quantitative and qualita tive analysis® cambial development in Meduilosa appears to have been remarkably similar to that which occurs in modern seed plants* In extant conifers and dicots with nonstoried wood® circum ferential expansion of the cambium is accommo dated by anticlinal division of the fusiform initials fol lowed by the enlargement of the daughter cells* The multi plicative divisions occur through the production of horizontal or obligue (pseudotransverse) cross walls. New fusiform initials in Medullosa were apparently produced by 168 anticlinal d i v i s i o n s in which an elongate oblique partition

Has formed® She length of the anticlinal partition in extant plants appears t o fee a direct reflection of the length of the dividing initial (Baonan, 1964* 1965) . Long* s t e e p l y angled partitions are formed when elongate initials d iv id e * and short* horizontal or low-angled partitions are produced in short cells® This general trend seems to hold f o r Hedullosa^ where b o th the fusiform initials and the cross walls appear to have been uncommonly long®

The number of new fusiform initials added to the vascu lar cambium in Medullosa is relatively low (approximately

0.64 initials per mm of radial growth)®3 Among other things, this may reflect the unusual morphology of the sec ondary xylem zone. The cambium associated with each vascu lar segment in Medullosa was more or less elliptical in transverse section® The small amounts of wood produced laterally in the segments suggest that cambial activity in these zones was lim ited, and most of the xylem was formed toward the inside and outside of the stem (Deleworyas,

1955)® The tangential tension on the developing cambium in such a system was less than that in circular camfeia since

3 Although comparable figures for extant plants have not been calculated, it is clear that the rate cf multiplica tive division in Medullosa is lowj Bannan (1950) report ed a net increase of 121 fusiform initials over a radial distance of 4-6 mm in a wood zone of limited tangential size. In addition, calculations utilizing Eguation No. 9 and the limited data provided by Bailey (1923) for Pinus indicate a rate of approximately 3 3-4 new fusiform ini tials added to the cambium per mm xylem accretion® 169

radial enlargement would have effected a smaller net change

in circumference® For example, if the elliptical cambium

had major and minor radii of 10 sm and 1 mm, respeciwely,

i t would have a c irc u m fe re n c e o f 44®9 mm (Fig® 9 8 )® An

increase of 1 mm in the minor cadius would change thecir

cumference to45®3 ms 0 an increase of 0®4 am or 0=9%® In

contrasty in a circular cambium with acircumference of

44®9 ms, a 1 ms increase in the radius mould change tbe

circumference to 50®1 mm, an increase of 6 mm or 13®43=

Thus, in the collective cambium of medullosan stems, a rel

atively large increase in girth could fahe place with lit

tle developmental change in the morphology of the meristei®

Evidence obtained in this investigation indicates that

cambial development in Medullosa was similar in many

respects to that which occurs in modern seed plants® This

does not imply, however, that these Carboniferous stems

developed according to conventional patterns of primary and

secondary growth® The occurrence in the vascular segment

of dimorphic tracheid bundles, the evidence of localized

meristematic activity, and the unusual anatomy of the sec

ondary sylem suggest that an unusual pattern of primary and secondary growth were present in stems of Medullosa® Addi

tional work focusing cn small specimens with limited secon

dary growth is needed to provide answers to guestioas regarding early stages of stem development in these unusual

Paleozoic plants. 170

CQaB&JgM,.jS

The secondary xylem in cordaitean stems has a modern ana tomical analogue in the wood of living Araucariaceae<> The structural sim ilarities include the narrowness and limited height of the rays* the absence of axial secretory canals* and the distinctive appearance of the intervascular pit ting® Despite these similarities* Jeffrey (1912) pointed out that there are numerous differences between the tao wood types that are often overlooked® These nottilthsband ing* the remarkable anatomical correspondence between the wood of cordaites and modern conifers suggests that the two

»ere formed according to a common developmental ground plan* In this respect* wood analysis of numerous extant conifers (Bannan, 1965* and references cited therein) has indicatd that the changes in sixe that occur during tracheid differentiation are minor* and it is reasonable to assume that a similar developmental pattern was present in the formation of cordaite aood.

The results of both qualitative and quantitative analy sis suggest that the vascular cambium in cordaite stems accommodated the increase in circumference primarily by the production and subsequent enlargement of new fusiform ini tials® As the lateral meristea was displaced radially by the centripetal production of cells* fusiform initials divided anticlinally. The orientation of the net# cross 171 w a ll was oblique* numerous studies have shown that such a developmental pattern predominates in the conifers*

Although Barman (1968) has observed that some of the multi plicative divisions in conifer Gambia are lateral ( i . e . , a partition forms that intercepts only one tangential w a ll)„ the vast majority can be classified as being pseudotran- s v e r s e .

Compared to Hedullosa„ the rate at which nets initials were formed in the cambium of the cocdaites was extremely high (approximately 33*0 new fusiform Initials for each mm in c r e a s e in ra d iu s ) * As n o te d e a r l i e r , comparable data regarding this aspect of cam bial development have not been calculated for extant plants* The limited information that is available, however, indicates that the rate in the cordaites is similar to t h a t i n extant conifers*

Tracheid lengths determined in t h i s study conform to the mean measurements proposed by Bailey and Tupper (1918) fo r the cordaites. The secondary elements in this group are also similar in size to those of the Araucariaceae, which along with the Taxodiaceae tend to have the longest tra cheids in the conifers (Bailey and Tupper, 1918; Carlguist,

1975). It is important to note, however, that no phylogen etic significance can be attributed to t h i s s i m i l a r i t y s in c e a v a r ie ty o f f a c t o r s including position and age (Bai le y and Shepard, 1915; A n d erso n , 1951; S p u rr and H yvarinea, 1954j Dinnoodie* 1961; Seth and Jain* 1976s Seth* 1981| * as well as the environment (Harlow* 1927; Keinholz* 1931; Lar son* 1964; Richardson* 1964; fan den Oever* Baas* and San- dee* 1981) are known to affect this parameter in extant plants,, The correspondence between the secondary tracheids in the araucarian conifers and the cordaites may be iapor- tant in that there appears to he a strong correlation between tracheary element length and overall plant size

(Carlguist* 1975)» It has been proposed that* within a group* lenger tracheids are found in tall* arborescent plants* and shorter tracheids are produced in plants of lower stature. The relationship seems to be a result of the different mechanical properties associated with tra cheids of different lengths. Longer elements fend to be stronger and more resistant to lateral stress than shorter elements (Carlguist* 1975). On the basis of the similarity of tracheid length between the cordaites and arborescent conifers* it is reasonable to suppose that at least some of the cordaites also possesed an arborescent growth habit.

Great care must be taken in this regard* however* since short pachycaulous g ymnosperms (i.e.* certain cycads including Dioon) also possess elongate tracheids (Bailey and Tupper* 1918; Carlguist* 1975). In these rather sguat axes* the elements have apparently been "released" from a mechanical function and presumably perform a specialized 173 r o l e in conductioa (Carlguist* 1975) 5 lon g tracheids* which exhibit extensive regions of overlap* are g e n e r a lly s e r e efficient in conduction than short elements,, Thus# the possibility that the c o r d a ite s sere shrub-like cannot be t o t a l l y r ejec te d * especially in vie® of the fact that they possessed a large parenchymat o us pith as ia pachyeauls«

SlBBBhl DISC 0531001

One o f th e most distinctive trends in the early evolution of land plants nas the pattern of increasing plant height*

During the period from the middle/late S ilu r ia n * when plants apparently first moved on to land (Edwards* Bassett* and Rogerson* 1979; Edwards and Feehan* 1980)* to the Car boniferous* the predominant growth habit shifted from low* herbaceous forms to arborescent and shrubby types. Fur th erm o re* by th e start of the Carboniferous* a l l o f th e major vascular plant divisions (lycophyta* Progymnospermo- phyta* Pteridophyta* and Sphenophyta) were characterized by arborescent forms (Barghoorn* 1S64)« Based on our current understanding of conditions during the middle Paleozoic* the tallest plants appear to have had a selective advantage b ecau se o f; 1| a dominant position in the competition for light; 2) a g r e a t e r likelyhood that wind-borne propagules would be dispersed over relatively large areas* and 3) a physical separation o f delicate plant parts (e.g .® le a v e s * 174 ovules* etc®) fro® phytophagous arthropods on the ground

(Saain* 1978) - flight in arthropods apparently did not develop until the late Devonian or early Carboniferous

(Sootton* 1976)® iBe rapidity sith tshich the shift from loH-groyiag plants to arborescent forms occurred (approxi mately 6D m®y® from the late Silurian to the late Devoni an) indicates the intensity of the selective pressure®

To a c h ie v e maximum h eig h t* f r e e - s t a n d i n g v a s c u la r p l a n t s reguire 1) an indeterminate* or at least long-lived* apical meristem* 2) large stem girth in conjunction with an ©icon ic groath form* and 3) organized cauline mechanical tissue

(sclerenchyma) to impart structural stability to the stem®

Bith reference to (2) and (3)* it is clear that the organi zation and arrangement of the xylem and auxiliary scler enchyma was intimately associated vith the evolutionary progression toward arborescence. Moreover* it is reason able to suspect that increasing histologic complexity should parallel this apparent trend® Such Has probably the case* and* focusing on the general complexity of stem anat omy over time (and not on changes Hithin individual lineag es) * there is a clear progression from the simple haplos- telic organization in rhyniophyte stems* to the stellate protosteles of Asteroxvlon, to the highly disected steles in species of cladoxvlon and Pseudosporochnos, These changes in stelar architecture progressively increased the 175

the surface area-to-volume ratio between the sclerified

mechanical tissue (xylem) and the surrounding ground tissue

thereby increasing the overall stem rigidity and creating

es in stelar anatomy there appears to have been a gradual

increase in the amount of accessory strengthening tissue in

the stem in the form of a continuous peripheral ring of

1962)= Studies of modern plants have shown that the maxi

mum girth and height of plants that grow solely by apical

activity is ultimately limited by the overall size of the

add mechanical/conducting tissue to the stem Mas virtually

unlim ited© and© th e re fo re © maximum height© d e fin e d on the basis of the physical limitations of biological systems

* It is important to note that© for the sake of simplicity© the discussion has centered solely on the mechanical com ponent of the primary xylem. ether features that are no less important in understanding patterns in stem evolu tion are the physiological relationship between cauline tissues (Boner© 1923© 1930; Carlguist© 1975) and the evo lution of foliar organs (Carlguist© 1975)= Moreover© this discussion is concerned only with those plants that were erect and self-supporting© and excludes procumbent and low-growing forms that were well-represented in mid- Paleozoic floras. 176

(Bower,* 1930)^ could be attained-. Based on the study o£ l i v i n g plants® it has generally been acknowledged that c i r culate re n t i a l enlargement of the vascular cambium Is brought about exclusively by division and enlargement of fusiform initials- The results of the present investigation® on the contrary® suggest that this was not universally the case® and that a variety of mechanisms sere present in the early arborescent plants to accommodate cambial enlargement- In an attempt to understand the nature of the differences between the cambia of modern plants and those in more prim i t i v e groups® it is relevant to examine the meristem in terms of the physical parameters that affect cambial devel opment and the structure/f unction constraints on th e d eriv ative xylem elements.

By virtue of the fact that the vascular cambium produces cells centripetally® the meristem is continually under com pressive stress in the radial plane and tensional stress in the tangential plane (Hejnowicz® 1980). The former is apparently critical in maintaining the integrity and organ ization of the meristem since cells of the cambium rapidly dedifferentiate when the pressure is relieved experimental ly (Brown and Sax® 1962; Brown® 1964)® There appear to be no structural modifications in the cells of the cambium to accommodate this stress® and it is maintained at relatively low® constant levels throughout growth- In contrast® if 177 the cambium is to remain circumferentially continuous* an active response to the presence of tangential stress is required ty the cells of the meristem. Shis fact was first comprehensively addressed by Bailey 11923)* who suggested a priori that cambial enlargement could result from an increase in the lengthy tangential width* and/or number of initials in the meristem. Subsequent analysis of the phe nomenon by Bailey indicated that changes in cell size were insufficient to account for observed cambial increase.

Thus it was concluded that anticlinal division of the fusi form initials was instrumental in accommodating tangential stress in the meristmaticaliy active cambium.

Extensive analysis of the frequency and distribution of multiplicative cell divisions in conifers (Bannan* 1950;

Whalley* 19 50; Srivastava* 1963) and angiosperms (Evert,

1961) indicate that the rate ox division is significantly higher than is required for circumferential enlargement.

The vast majority of ''superfluous" initials subdivide to form rays or are simply lost from the meristem. Further more* most multiplicative divisions occur at the end of an annual increment of growth (Bannan* 1950* 195 1* 1960a*

196h; Evert* 19 61; Cumbie* 1967). In fact * Eannan (1960b) concluded t hat * although anticlinal division of the fusi form initials is critical to the normal functioning of the cambium* the rate at which new initials are formed is not directly related to circumferential expansion. 178

Recent studies that have examined tracheary element nor- phology have shown that cell size has a direct tearing on the functional properties of the wood {Carlguist® 1975s

Zimmermann® 1983). Moreover® there is abundant evidence to indicate that trends in tracheid morphology within a taxon can he explained on the basis of different environmental conditions at the growth site (Harlow® 1927; Holz® 1931

Keinholz® 1931; larson® 1964; Richardson® 1964; Bannan®

1964)« Since wood functions both la a mechanical and con ductive capacity® any attempts to evlauate cell morphology must take into consideration both of these factors {Bailey®

1958) • In general® when all ether structural features remain constant® an increase in cell length results in increased strength and more efficient conduction (Siau®

1971; Carlguist® 1975). In contrast® enlargement of cell diameter reduces mechanical strength® but increases conduc tive efficiency {Zimmermann® 1982® 1983). Variability in this parameter within a stem is generally a result of vari ations in the radial enlargement of the cells during dif ferent iat ion. There Is usually little change in the tan gential width of the elements during wood development.

Superimposed on these general structure/function patterns is the concept of wood ** mesomorphy" {Carlguist® 1977; Carl g u i s t and Debuhr® 1977) or® more p re fe ra b ly ® wood s a f t e y

(Zimmermann® 1982® 1983}. T h is p a ra m e te r m easures th e 179 capacity cf the wood to localize aix embolisms caused by frost* herbivory* etc®* and thus reduce the detrimental effects of cavitation® Although saftey is a function of several aspects of wood structure* when comparing morpholo gically similar woods those with shorter narrower tracheary elements tend to be more resistant to cavitation than those with longs, broad elements ® 3 Thus* patterns in the length and width of tracheary cells ia the wood can he interpretted in the context of changing mechanical and physiological/ecological properties during development®

This is particularly well illustrated in the differences in cell size that occur across an annual increment of radial growth in conifers. The relatively aide tracheids in the spring wood are specialized for conduction* and the narrow er elements in summer wood are stronger and more resistant to the effects of freezing and drought (Carlguist* 1975).

In addition* the gradual increase in cell length that gen erally occurs across the growth ring dictates that the longest cells will be formed in the summer wood* thus pro viding additional mechanical strength to that region. The increased freguency of multiplicative division in the cam bium near the end of the growth cycle results in an abun dance of short cells in the last-formed summer wood and

s An equally important component of the wood that is affected by tracheid size is the capability to resist high negative pressures that develop within the cells during periods of water stress. 180 first—formed spring wood* making these zones less sucep table to the effects of cavitation®

The role of anticlinal division in regulating tracheary element length and the apparent form/function relationships in the secondary tracheids provide some insight into under standing the sim ilarities and differences in the camfcia of fossil and extant groups® A centripetal increase in fusi form initial/tracheid size in the inner wood is relatively common in l i v i n g p l a n t s (B ailey* 1920? C a r l g u i s t * 1975)®

Carlguist (19 75* 1980) proposed that the trend signifies the increasing conductive and mechanical strength require ments in the wood of the developing plant® An alternate interpretation for this phenomenon was suggested fcy Phiiip- son and Butterfield (1967)* but this was later shown to be invalid (Baas* 1976)- The increase in cell length in seed plants is accompanied by anticlinal division of the fusi form initials* and the change in size appears to be regu lated to some extent® Presumably any change in the growing conditions results in modifications in tracheid morphology to yield the optimum cell structure for the given condi tions® In the cryptogams examined in this study* cell enlargement occurs without accompanying anticlinal divi sions* and* in the absence of a mechanism to reduce cell size* the resulting tracheids are extraordinarily long and broad. The increase in cell size in these plants was 181 apparently governed exclusively fey tensional stress in the

cambium. Since such stress results fro® the increasing

radius of the meristem, the ra te of cambial cell enlarge

ment was ultimately related to the extent to which aea

c e lls were produced centripetally- Based on the extreme

length and width of the cells, the elements a lm o s t c e rtain 

ly represent forms specialized for efficient conduction.

Such an unusual morphology mas probably of high selective

value in the extremely aesic conditions of the Carbonifer ous coal stamps. Furthermore, the utility of such cells

would have been high in axes that were not self-supporting

(e- g., Sphenophyllum, Stiomaria. Arthropitvs deltoides)

or that possessed alternate systems for providing mechani cal rigidity (e.g., lepidodendrid and aedullosan stems).

Of all the cryptogamic woods examined in this study, the structure and development of the secondary xylem in

Arthropitys communis appears to conform most closely to

that in seed plants, in particular the conifers. Not only are the tracheids in this plant similar in size to those of the conifers, but there was also a systematic mechanism, a l b e i t determinate, for increasing the number of fusiform initials in the cambium. Ihe general morphological corre

spondence between the tracheids of calamites and conifers suggests that the cells in A. communis were functional in providing mechanical strength to the axis as well as in the conduction of water. In contrast* the structure and devel opment of the wood in Medullcsa is superficially unlike that of seed plants and conforms more closely to that of contemporaneous pteridophytes® The tracheids in this plant are presumably among the largest of any seed plant and cor respond closely to those of the arborescent lycopods® The form of the cells suggests that they played a specialized role in water conduction. &id.nl support was apparently derived from the unusual arrangement of the vascular seg ments and the presence of fiber bundles in the cortex and secondary phloem® Although there is good evidence for the occurrence of multiplicative divisions in fusiform initials of fledullosa® the process appears to have been weakly developed® Despite these interesting parallelisms in the

Carboniferous seed plants and cryptogams* it remains clear that there is a consistent structural distinction between them in the process of cambial development® Plants in the latter group lacked the capability to reduce the size of the initials during wood production. The absence of such a mechanism dictated that the wood In these plants develop according to a rigid scheme in which tracheid size was determined by physical* rather than biological* con straints® This lack of ontogeatic flexibility presumably prevented them from adapting to short term fluctuations in climatic conditions and no doubt contributed to the demise of the arborescent cryptogams in the late Paleozoic® 183

The value of cambial analysis in phylogenetic studies cannot be adequately assessed based solely on the results of the present investigation® . Critical to evaluating the use of this technique in sys tenia tics studies is a more thorough understanding of the structure/function con straints within the stem* the developmental limitations of lateral growth g and the relationship between cambial devel opment and growth habit® In this respect* the problem of whether or not similar cambial patterns occur in plants with similar growth habits needs to be addressed® Such may a phenomenon may have been present in Carboniferous spheno- phytes* for example* where Arthropitvs deltoides and

SphenophyHum plurifcliaturn are developmenta 1 1 y more simi lar to each other than A®, del to ides is to A®. communis®

At present it cannot be determined if this unusual situ ation reflects parallelism resulting from similar growth habits or if it is indicative of a close phylogenetic affinity® Detailed information about the reproductive structures in these plants is required before an adeguate solution to this problem can be attained® Nevertheless* developmental analysis of the cambium seems to hold promise as a method for better characterizing major plant groups and providing a more thorough understanding of the evolu tion of the arborescent habit® C h a p te r I

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a p s b m i x n

T a b le 1

Developmental Data

Us. brevif clius #99 r a d iu s primary xylem = 1 1 . 0 mm radius secondary xylem = 27.0 mm

PERCENT COMPOSITION LEAF TRACHEID RADIUS TRACE TRACHEID RAY NUMBER LENGTH DIAMETER IJS is) (%i {%) i%) (cells) (mm) (mm)

13. 4 1 95 4 103.0 8 . 8 . 089£.0 13 14.4 1 94 5 8 4 .6 1 0 . 6 .096 4.0 11 15.4 1 95 4 7 2 .0 1 2 . 1 .1 0 6 4 .0 1 4 16.4 ? 94 5 7 3 .5 1 2 . 8 - 1044.012 17.4 1 95 4 7 5 .7 13.4 .103& .013 18. 4 1 95 4 7 5.6 13.9 . 1 05&.Q 10 19.4 95 4 7 2 .6 14.3 .1 1 2 4 .0 1 6 20.4 1 95 4 7 3 .3 15.1 .1 1 U .0 1 5 21.4 1 94 5 6 8 . 0 15.5 . 1204.020 22.4 1 94 5 7 1 .8 15.9 J 17*.016 24.4 1 93 6 7 1 .2 15.9 . 1254.016 25.4 1 93 6 7 4 .4 16.2 .1244*018 26.4 1 94 5 7 8 .0 16.3 .1 2 4 a . 015

- 201 - 202

Table 2

Developmental Data

Po brevifclius #104

radius primary xylem = 1 . 0 n radius secondary xylem = 24.0 mm

PERCEPT COMPOSIT10M LEAP TRACHEID ilDIOS TRACE TRACHEID RAJ DUMBER LERGIH DIABETES (mm} (%} (35) 1%) fe e lIs} (ma) (mm)

1 0 = 0 1 90 9 2 2 .5 1 7 .9 -1 4 2 4 .0 2 2 1 1 . 0 1 90 9 2 2 . 2 19.4 .1 4 6 4 .0 2 6

1 2 . 0 1 93 6 2 2 .9 2 1 . 8 . 1424.025 13=0 1 90 9 2 3 .7 2 2 .7 .1 3 8 4 .0 3 4 14.0 1 91 8 24. 1 23.5 . 1434.033 15.0 87 1 2 2 6.3 2 1 . 6 .1 4 6 4 .0 2 9 16.0 1 81 18 4 0 .7 15.0 . 1354.026 17.0 1 85 14 5 4 .4 1 2 . 6 .1 3 4 4 .0 3 1 18.0 8 6 13 7 0 .8 11.3 .1 2 3 4 .0 1 4 19.0 1 83 16 6 3 .9 13.2 » 1194.021 2 0 . 0 1 84 15 76. 1 11.9 .1184.029 2 1 . 0 1 89 1 0 7 5 .4 12.7 .1 2 4 4 .0 3 9 2 2 . 0 1 8 6 13 7 3 .0 13. 4 .1 2 3 4 .0 2 0 23.0 1 8 6 13 73.4 14.4 .1 1 9 4 .0 2 2 2 4 .0 1 8 6 13 8 2 .7 1 2 . 8 .1 2 4 4 .0 2 1 203 Table 3

Developmenta l Data

£s. b re v if c l i u s #129 radius primary xylea = 1 1 . 0 ma radius secondary xylea = 32.0 am

PERCENT COMPOSITION LEAF TRACHEID RADIUS TRACE TRACHEID RAY RUBBER LENGTH DIABETES Cam) {%) 1%) (%) ( c e l l s ) (am) (mm)

1 1 . 0 1 94 5 4 2 .7 16.6 .0 9 3 4 .0 1 9 1 2 . 0 1 92 7 4 5 .6 17-0 .0 9 0 $ .0 3 0 13.0 1 92 7 6 0 .0 14.9 -085& .016 14.0 1 91 8 7 8 .0 13.3 .0 7 8 1 .0 1 6 15.0 1 93 6 5 5 .8 15.1 . 1051.024 16. 0 1 94 5 49 .6 18.5 .1 0 1 1 .0 1 7 17.0 1 93 6 50. 2 19 .4 . 103t«018 18.0 1 94 5 5 7 .3 19.4 .1 0 4 t . 018 19.0 1 93 6 56. 1 19.6 - 1021.019 2 0 . 0 1 94 5 58.3 19.7 .1 0 4 1 .0 2 0 2 1 . 0 1 94 5 59. 1 19.8 .1 0 6 4 .0 2 2 2 2 . 0 1 95 4 59. 1 1 9 .8 .1 0 6 1 .0 1 5

2 3 .0 1 93 6 57. 3 2 0 . 8 .1 1 4 4 .0 1 7 2 4 .0 1 93 6 5 4 .7 21-4 . 12 14.024 2 5 .0 1 92 7 53.7 2 1 . 6 .1 2 6 4 .0 2 1 26.0 ? 93 6 5 4 .8 2 2 . 6 -1 2 4 4 .0 2 3 204

Table 4

PeyeloEffiental Data

P. breviJfolius #1 536 radius primary xylem = 1 2 . 0 mi radius secondary xyleo = 40.0 mm

PEBCE1 T CCHIOS1T20U LEAF TRACHEID RADIUS TRACE TRACHEID RAY NUHBEB LEMGIH DIAMETER (mm) {%} (*) (%l ( c e lls ) (mm) (am)

16.5 1 93 6 63.9 14.0 . 109i.0 1 7 19.0 1 93 6 56. 1 16.0 . 125*.019 2 1 . 0 1 92 8 57.8 17.5 .120 *.024 2 3 .5 1 90 9 61. 4 17.8 .123*.024 2 6 .0 90 9 68.3 18.3 .1 1 9 * .0 2 8 2 7 .0 1 8 8 1 1 65.0 18.3 .127*.021 2 8.0 1 84 15 59. 1 19.3 .1 3 1 * .0 2 6 2 9 .0 1 87 1 2 60 .0 19.9 „ 134*.020 3 0 .0 1 90 9 63.8 19.9 .1 3 5 * .0 2 3 3 1 .0 8 8 1 1 60.6 2 0 . 6 . 139*.022

32.0 1 8 6 13 63.7 2 0 . 8 . 1324.021

3 3 .0 1 87 1 2 71. 3 2 0 . 8 .1 2 3 * .0 2 3 3 7 .5 1 82 17 209.0 9.0 . 1044.019 3 8.5 1 82 17 148.4 12.3 .1 1 0 4 .0 1 8 3 9.5 1 82 17 145.5 1 1 . 8 .1 2 0 4 .0 1 8 4 0 .0 1 83 17 128.9 14.2 .1144.014 205 Table 5

Developmental Data

JL» breyif d iu s #1712 radios primary xylem = 9.0 mm r a d i u s se c o n d a ry xylem = 26®0 i s

PERCENT COBPOSITION LEAF TRACHEID RADIOS TRACE TRACHEID HAY NUMBER LENGTH DIAMETER

(mm) <*j (8 ) (%) ( c e lls ) (mm) (mm)

1 1 . 0 1 93 6 56.6 14.0 .0 8 2 1 .0 13 1 2 . 0 1 92 7 52.9 15.6 .0 8 5 1 .0 1 4 13.0 1 8 8 1 1 4 7 .7 16.4 .0 9 3 4 .0 1 8 14.0 i 92 7 4 5™ 3 17.9 . 1 0 1 1 . 0 2 2 15.0 i 92 7 4 5 .2 19.0 . 1021.017 16.0 i 94 5 4 6 .6 19 .9 .1 0 3 1 .0 2 0 17.0 i 30 9 4 7 .0 2 1 . 1 .0 9 8 1 .0 2 0 18.0 i 92 7 4 4.3 2 1 . 6 . 1 1 0 1 . 0 2 1 19.0 1 92 7 4 4 .9 2 2 . 1 .1 1 2 1 .0 1 9 2 0 . 0 i 91 8 4 2 .4 23.3 .1 1 7 1 .0 1 9 2 1 . 0 1 8 6 13 4 2 .6 23.4 .1 1 5 1 .0 1 9 2 2 . 0 i 89 1 0 46.3 2 4.2 - 1 1 1 1 . 0 2 1 2 3 .0 i 87 1 2 4 5 .5 24.3 .1 1 5 1 .0 2 1 24.0 1 87 1 2 45.2 2 4 .9 . 1 1 8 1 . 0 2 6

2 5 .0 1 80 19 43. 1 25.0 - 1 1 8 1 . 0 2 1 206

T ab le 6

Developmental Data

P-. brevif clius #7249 radius primary xylem = 6-0 ms radius secondary xylem = 17-0 ms

PERCENT COMPOSITION LEAP TRACB1JD 1DXUS TRACE TRACHEID BAY NUMBER IENGTH DIAMETER (am) {%} (*) (%} ( c e lls ) (mm) (mm)

6 - 0 1 93 6 33-1 1 2 - 6 - 085 $-0 16 7-0 1 92 7 27-1 15-9 -095 £-018 8-3 1 92 7 29 -6 16-9 - 097*-019 9-0 1 92 7 29-3 17-6 -1021-018 1 0 - 0 1 87 1 2 28-4 18-7 - 1041-022 1 1 - 0 1 92 7 31-3 19-0 -1081-015 1 2 - 0 1 8 8 1 1 29- 1 19-7 -117 1 -0 1 5 13-0 1 89 1 0 3 3-5 19-8 -1111-014 13-5 1 80 19 29-4 20-5 -1 1 4 1 -0 1 7 207 Table 7 Developmental Data

£2 . brevif clius #8899 radios primary xylea = 8,0 ms radius secondary xylea = 14.0 .1 1

PERCENT COMPOSITION LEAF TRACHEID RADIOS TRACE TRACHEID RAY NUMBER LENGTH DIAMETER (mm) {%) (%) (%l ( c e lls ) (am) ( mm)

8 0 2 1 94 5 82.2 9.3 .0 6 4 ± .0 11 8.5 1 93 6 55 .5 1 1 . 6 . 0781»014 8 . 6 1 94 5 47. 2 13. 1 ® 0834.014 9 .2 92 7 4 4 .4 1 4.6 .083& .015 9.4 1 93 6 4 0 .3 14.8 . 093±»0 17 9 .6 1 94 5 3 9 .6 15.9 . 0913:.0 17 9 .9 92 7 41. 5 16.0 .0 8 7 4 .0 1 5 1 0 . 1 1 93 6 39 .3 1 6 .9 .0 9 0 4 .0 1 8 1 0 . 2 1 91 8 3 4 .3 17.2 . 1003-017 1 0 .4 1 91 8 3 7 .5 17.4 .0 9 2 3 .0 1 6 1 0 . 6 1 87 1 2 3 3 .8 17.7 .0 9 8 4 .0 2 0 1 0 . 8 1 8 8 1 1 3 3 .3 1 7.8 . 1024.019 1 1 . 0 1 93 6 36. 5 18.0 .0 9 9 4 .0 1 7 1 1 . 2 1 90 9 38.9 18.1 .0 9 1 4 .0 1 6 11.4 1 93 6 38. 1 18.2 .0974.015 C&iajpter WX

a bpeh d is e

T ab le 8

Deve lopmental Data

S-2_ fico id es #20 98

primary xylem radius = 4.0 u> secondary xylem radius = 10.5 mir

PERCENT COMPOSITION BT KCOD TRACHEID RADIUS RMS RAYS TRACHEID NUMBER LENGTH DIAMETER (mm) (%) (%) (c e lls ) (mm) (mm)

7.6 14 3 78 12 24.C .. 1221.022 7.3 13 8 79 13 23 .7 .1 1 3 1 .0 1 7 7.0 13 6 81 13 22 .8 . 1171.02C 6,7 12 5 83 13 22.2 .1251.019 6.5 11 4 85 14 22.. 1 . 1121.020 6.2 12 4 04 14 21.,2 ..1131.019 5 .9 11 5 34 13 20.4 .1 1 9 1 ,0 1 9 5 .6 12 4 84 14 18.9 ..1121.019 5.3 11 4 85 • 16 17. 3 . 1011.021 5.0 11 4 85 15 16.4 ..1071.022 a . 7 10 6 84 19 13.6 ..0951.018 4.5 9 9 02 25 11 .4 .»0791.020 4.3 9 11 80 35 9,3 «. 0661, 016

- 208 - 2 09

Table 9

Develocmental Data

S._ f i c o i d e s #6 5 26 primary xylem radius = 6,8 mm secondary xylem radius = 12,8 sum

PERCENT COMPOSITION ET MOO C TRACHEID RADIUS RAYS RAYS TEACHEIC UMBER LENGTH DIAMETER (am) m (%) (5) ( c e lls ) (mm) (mm)

12,6 12 6 82 33 16-6 - 118*.023 11-9 13 6 81 33 16-4 „ 11 1±. 027 1 1-2 1*4 3 83 31 16.. 2 -1 1 5 &-018 10.5 13 7 80 31 15.7 - 1094-016 9-8 13 4 83 29 15.. 2 ..1144,023 9., 1 13 7 80 32 14.. 5 . C9 84.019 8. 4 15 5 80 29 1 3 ,8 . -1064.028 7 .7 15 9 76 37 12-5 .0784.014 7 .0 18 12 70 38 11..6 «0664-016 Table 10

Dev elotmental Cat a

S . f i c o i d e s #6 699 primary xyleiu radius = 3.4 nrm secondary xylem radius - 7.7 mm

PERCENT CCRPGSITIC N ET EGO D TflACHEID {ADIUS R AYS RAYS TEACHEID NUMBER LENGTH DIAMETER (mm) (X) (%)

3. a 33 7 80 50 5.1 . 06 9 ±M 0 17 4.1 13 9 78 38 6. 3 .. 0821.019 4. 5 13 4 83 29 7.8 » 1QU.025 4.9 12 3 85 28 8 .8 . 1061.024 5. 3 11 2 85 24 10.. 6 .1 1 1 4 .0 1 4 5.7 12 3 85 23 11.7 . 1134. 023 ■6. 1 12 2 86 22 12.. 4 .1 1 8 4 .0 19 6.6 11 2 87 22 13.7 . 1214,. 02 3 6. 9 11 2 87 22 14.1 .1 2 3 4 .0 2 5 7.3 12 3 85 21 15. 7 . 1194.018 7. 5 13 4 3 3 20 16.0 .1 2 4 4 .0 1 8 Table 11

De v e 1 o preen ta.1 Data

S. ficoldes #8521 primary xylem radius = 6.3 mm secondary xylem radius = 18.3 mm

P ERCENI COMPOSITION RT ROOD TRACHEID RADIOS RAYS RAYS TRACHEID NUMBER LENGTH DIAMETER (mm) I%) (%) (%) ( c e lls ) (mm) (mm)

6. 5 11 9 80 110 4-2 ,064 £ -0 19 7„5 9 7 84 36 1 0-9 -1001- 023 8o 5 8 5 07 27 14- 1 .1 2 0 1 .0 4 1 r 9., 5 8 “O 86 24 16-8 .1 2 9 ^ .0 4 0

1 0,. 5 10 7 83 22 18,9 - 1 2 7 l„ 018 1 1.. 5 11 6 83 24 19-9 .1271-023 12-5 12 7 81 24 20-7 - 1261,023 13., 5 13 6 81 24 21-6 -1 3 1 1 ,0 2 8 1 4.5 12 7 81 25 22- 1 - 13 4 ±„ 0 2 8 212

Table 12

Developmental Data

S. ficoides #8749

primary xylem radius = 4.2 mm secondary xylem radius = 14.7 am

PERCENT COEPOSITION ET K COD TRACHEID RADIUS RAYS RAYS TRACHEID HUMBER LENGTH DIAMETER (in m) (?) {%) r o ( c e lls ) (mm) (mm)

5. 5 13 11 75 28 11-2 .0854:.0 18 6.5 12 10 78 22 1 3 .0 .112-1.027 7 .5 11 9 80 24 14.0 .1 1 0 1 .0 2 1 8. 5 10 o 84 26 13.4 .1 2 7 1 .0 1 8 9.5 10 8 82 26 14.8 - 1291.024 10. 5 10 7 83 28 1 6.0 .1 2 3 1 .0 2 1 11.5 11 5 04 29 17.0 .1 2 4 1 .0 1 8 12.5 11 8 81 30 16.7 .1271.020 Chapter fill

T ab le 13

Develoomental Data

So plurifoliatum #209 primary xylem radius = 0. 8 mm secondary xylem radius = 3.2 mm

TRACHEID TRACHEID TRACHEID RADIOS LENGTH DIAMETER NUMBER (mm) (mm) (mm) ( c e lls )

1.0 1 3 -7 ± 6 -4 -1 3 3 * .0 3 8 0.57 1.2 14.7*6.0 . 14 31. 0 2 9 0.60 1. 3 15-9*5.6 - 167*.021 0-51 1-5 17-6*5.3 .168*«022 0-53 1.6 1 9 .4 * 4 .6 . 1 68*.® 017 0-51 1.7 22.5*2.8 - 162*.023 0-49 1.9 22.5*4.2 .164*.025 0.54 2 -0 2 3 .7±3„7 . 156*. 017 0. 57 2-2 25.013.4 -162*.027 0.57 2 -5 2 5 -7 * 3 .4 - 171*. 020 0.60 2-6 26-9*3.3 .177*.024 0.57

- 213 - 214

T ab le 14

Developmental Data

S. plurifoliatum #2539 primary xylem radius = 0.5 am secondary xylem radius = 2®1 mm

TR&CHEID TBACHEID TBACHEID IDIUS LEDGTH DIAMETER H0MBEB (mm) C mm) (mm) f e e l Is)

Oo 6 1 3 .3 4 4 .3 .0 9 3 4 .0 1 9 0.51 0 .8 12-5t1-3 . 1054.021 0.64 0® 9 1 2 .3 4 3 .2 .1 1 3 4 .0 2 9 0.68 1.1 1 3 .0 4 3 .7 . 1314.029 0.68 1.3 1 4 .3 4 3 .5 .1 2 9 4 .0 2 5 0.74 1-5 16.043.5 . 150 4. 023 0.65 1.6 1 6 .3 4 3 .6 .1 5 2 4 .0 2 5 0.68 1-8 1 6 .0 4 4 .0 . 1524.019 0.77 2 .0 1 9 -2 4 3 .4 .1 4 8 4 .0 1 7 0.74 2 .1 2 1 .0 4 4 .0 . 1554. 012 0.68 215

T a b le 15

Develocaeatal Data

S. plurifcliaturn #6620

primary xylem radius = 1.1 mm secondary xylem radius = 4.9 mm

TRACHEID TRACHEID TSACHEID iDIUS LENGTH DIAMETER NOMBER [mm) (mm) (mm) ( c e lls )

1 .3 16 . 1 3-2. 6 - 107 ±.019 0.79 1.4 17.312.4 .097*.011 Oo 87 1.6 17.9*2.2 , 099 *.020 0.94 1.8 18.4*2.5 .122*.025 0.84 2 .0 19.0*2.8 . 115*. 022 0 .9 6 2.2 19-2*3.0 .1 2 5 * .0 2 8 0.96 2 .4 19.9*2.7 . 132*. 025 0.96 2 .6 2 1 .1 * 2 .9 » 1 40*.041 0.92 2 .8 21.9*2.9 . 150*. 032 0.89 3 .0 22-8*3.4 .137*.034 1.00 3.2 23.7*3.4 . 133*. 033 1.06 3.4 2 5 -0 * 3 .7 » 139*. 024 1.02 3 .6 25-5*3.7 . 144*. 024 1.03 3. 7 26-2*3.5 .151*.033 0.98 4 .0 27-1*3,6 . 154*. 024 1.00 4.2 28-6*3.7 .156*.035 0.99 4.3 29.0*3.6 • 159*. 026 0.98 216

S a b le 16

Developmental Data

So plurifoliatum #6649 primary xylem radius = 0.8 am secondary xylem radius = 1.8 mm

TRACHEID TRACHEID TRACHEID RADIUS 1EUGTH DIME SEE RUBBER (mm) (mm) (mm) ( c e lls )

1.0 1 4 .6 1 8 .0 .0 9 9 1 .0 2 7 0.72 1.1 14.8*8.1 . 1101.025 0.71 1. 3 1 4 .3 ± 8 -4 „ 111*. 01 9 0.86 1.4 1 5 .2 * 9 .1 . 1221.027 0.79 1.6 1 6 .3 * 1 0 .0 .1 2 5 1 .0 2 7 0.82 1.8 16.01-10.7 . 1411.036 0.84 1.9 1 8 .3 1 1 1.9 .1451.021 0.75 2.1 17.8*11.3 . 1391.020 0.89 2.2 1 5 .2 1 8 .4 .1481.017 1.02 2 .3 1 6 .3 * 8 .2 . 1601.019 0.92 217

T a b le 17

Developmental Data

5= plurif alia turn #8525 primary xylem radius = 1-0 mm secondary xylem radius = 4-3 as

THACHEID THACHEID THACHEID HADIOS LEKGTH BIAMETEB HUMBER Com} ( mm) f El) ( c e lls )

1-1 12-7 - 129*. 025 0-70 1-3 14-1 - 114*.025 0.85 1-6 1 4.5 . 113*. 026 1-02 2 -0 16.2 - 132*.016 0-98 2 .7 18.6 - 142*. 012 1-07 3-2 2 7 .2 -1 5 1 * .0 1 6 1-05 3 .9 22-9 . 147*. 018 1-21 4 .3 23-4 - 154*.016 1-25 219

Table 18

A. communis stem #2017 primary xylem radius = 13-4 mm secondary xylem radius = 27-4 mm

TRACHEID FASCICULES BEX RADIUS BOBBER LENGTH DIABETES NUMBER LENGTH D1AHE1ER (mm) ( c e lls ) (JDIS) (mm) (X10C0) (ram) (am)

27-4 422 5.6*1.4 - 042*.007 9-4 1314-047 -0544-014 27- 0 407 6 .1 * 1 .0 .04 0*-008 8-6 ©1364-046 - 054*.014 26-0 363 6.0* 1.1 .0 4 1 * .0 0 7 10-6 1294-045 -049±-015

25-0 319 6-2 *1-0 .042*.006 8-9 <9 1384-034 -053*-014

23-5 309 6 .2 * 0 .9 = 042*.005 8-0 49 161*-056 -0454-009 23-0 342 5 .8 * 1 .2 .041 *.008 8. 4 1404.046 -0464-011 22-0 353 5-6*1.2 -0384.007 7-8 13 9**046 .0 5 0 * .0 1 4 20-5 323 5 -8 * 0 .8 - 0 4 U .0 0 6 6-5 161*.041 -0414.007 19-5 330 5 -4 * 1 .1 - 039*-007 7-1 1694-067 -0374-008

17-0 315 5 .1 * 1 .1 .0 3 8 * .0 0 9 5-2 a t 1684-045 -0394-008 16-0 270 5,1*0.7 -037*-C08 5-2 164*.063 -0324-005 15-0 261 4 -8 * 0 .9 • 034*. 007 4-3 1644-060 .0 3 2 * .0 0 5 14.0 268 4 .0 * 0 -8 .0 3 6 4 -0 0 6 3-9 9 1954-059 -0274-005 13—5 291 3.8*0.5 . 032*- 006 2-7 227*.077 -0 2 4 4 .0 0 5

PERCENT COHPOSITION RADIUS XNTEEF ASCICU LAB FASCICULAR (mm) BAY TRACHEID BAY

28-0 4 58 38 27-0 4 59 * 37 2 6 .0 4 55 41 25-0 5 53 42 23-5 6 55 39 23- 0 6 56 38 2 2 -0 6 59 39 20-5 7 60 33 19-5 7 57 36 17-0 11 57 32 16-0 22 51 27 15.0 30 46 25 14-0 33 44 23 13- 5 40 42 18 220

T ab le 19

Developmental Data

4s. communis stem #6542 primary xylem radius = 16.0 mm secondary xylea radius = 40=0 is

TRACHEID FASCICULAR BAY RADIUS NUMBER LENGTH DIAMETER NUMBER! LENGTH DIAMETER (mm) ( c e l l s ) (mo) (01) (xlQGO) (mm) (mm)

16.1 248 4.1 o 033 ■&. 005 2® 1 . 190&.084 .0 2 3 * .0 0 5 16. 5 3 SO 3 .3 =0344.006 4=3 o 132*.041 .0 3 2 * .0 0 5 17.. 0 292 4 .9 .031*.006 7.5 .1 1 9 * .0 4 3 .0 3 1 * .0 0 8 17.5 284 5 .1 „ 034±. 007 9.6 .092*.029 .032*.007 18.0 334 4.8 .033±.006 10.3 .097*.030 .0301.007 18o5 2 99 5 .7 .035 ±.007 10.6 .0 9 5 * .0 2 9 .0 3 3 * .0 0 7 19.5 368 5 .4 .0 3 4 * .0 0 7 13.9 « 1 00*.043 .0311.008 20.0 385 5.7 .034±.006 13. 7 . 092*.023 .0324.009 20. 5 350 6 .5 . 034±®007 14.3 ®092*.029 .032*.008 2 1 .0 360 6.2 .035±.007 13. 1 .095*.050 .0 3 5 * .0 0 7 21 .0 281 6=5 .0 3 7 * .0 0 7 15.5 .102*.042 .0364.008 2 2 .5 368 5„9 . 036*. 007 15.8 . 091*.031 .039*.009 23.0 400 5® 7 .0 3 7 * .0 0 6 12.4 .100*.032 .0 4 3 1 .0 1 0

______PERCENTCC M P O S X T IO H ______RADIOS INTERFASCICULAR FASCICULAR (mm)______RAY THACHEID______RAY

16. 1 57 34 9 16.5 40 42 18 17.0 32 41 27 17.5 29 45 26 18.0 26 47 27 18.5 20 51 29 19.5 9 56 35 2 0 .0 8 60 32 2 0 .5 7 60 33 2 1 .0 5 51 44 21.0 7 60 33 2 2 .5 5 55 40 23® 0 4 60 36 221

T a b le 20

Developmental Data

Us. communis stem #6643 primary xylem radius = 17-2 mm secondary xylem radius = 30.2 as

IRACBEXD______FASCICULAB BAY !ADI OS NUMBER LENGTH DIAMETER NUMBER LENGTH DIAMETER (mm) ( c e l l s ) (mm) (mm) SxlOCO) (mm) (mm)

2 6 .7 367 6.1±0.7 .041 ±.007 10. 3 O 1054.027 o 061i . 01 • 2 6 .5 350 6.3±0»9 . 040±® 007 11.8 C3 1074.033 .0534.01 26.2 346 6 .1 ± 0 .9 .0414.006 11™ 4 CD1144.033 .0 4 9 4 .0 0 2 5®, 2 429 5 .8 ±0.9 .0374.007 10.3 © 3134.036 .0 4 6 4 .0 0 2 4.7 477 5 .2 * 1 .2 .0 3 4 4 .0 0 6 11-2 6» 115*.033 .0 4 5 * . 00. 24 .2 372 6 . 0 4 1. 2 .0 3 7 4 .0 0 8 9 .8 69 1134.032 .0 4 6 1 .0 0 . 23. 2 381 5.5 * 1.1 .0374.006 10.2 .0126±,038 .0 4 3 4 .0 0 . 2 2 .2 341 5 . 6 i U 1 „0374.007 10.0 a 1224.036 .046*.01 2 1.2 390 4.7*1.5 .0 3 5 4 .0 0 7 9 .3 m1324.044 .0 4 0 4 .0 0 . 2 0.2 320 5.6 *1.4 .0 3 3 4 .0 0 7 6 .7 «162*. 0 55 « 03 74.00 19.2 253 5 .0 * 1 .5 .0374.006 4.4 «» 182*.064 .0364.00.

______PERCENT COMPOSITION______RADIUS INTEEFASCICULAR FASCICULAR (mm) RAY______T BACHEIE______RAY

26.7 6 55 39 2 6 .5 7 53 40 26.2 8 52 40 25.2 8 58 34 2 4 .7 8 54 38 2 4 .2 8 52 40 23. 2 9 53 48 22.2 9 51 40 2 1 .2 15 48 37 20.2 21 47 32 19.2 37 39 24 222

S a b le 21

Developmental Data

JU cominim is stem #7037 primary xylem radius = 19.0 mm secondary xylem radius = 41.2 mm

TRACHEID FASCICULAR RAY RADIUS NUMBER LENGTH DIAMETER NUMBER LENGTH DIAMETER {mm) ( c e lls ) (am) (mm) (x 1000) (mm) (mm)

30. 0 6C7 5.6&G.9 «035±.OQ6 1 S.. 2 .1 01 4.037 .0 4 0 4 .0 1 29*0 446 5 .8 t 0 .7 .0 3 5 4 .0 0 6 14. 8 .123 4.030 .0481.01 28. 0 475 5.7 ±1.1 .035s.005 13.9 .1274.041 .0394.00 27. 0 533 5 -3 * 1 -0 .0354.006 11.7 .1354.043 .0374.00 23. 0 464 5.0& 0.8 .036& .006 11- 1 • 1291. 045 .0 3 3 4 .0 0 21.5 393 5.2±0»4 .0364.006 9.5 «1264-056 . 0331. 00. 19.5 260 4 .6 40.8 . 0331. 005 5 .8 .1 5 3 4.055 . G254.0 0 19® 3 278 3-6±G-5 .032t.004 3.8 -1 5 4 4 .0 5 3 .0 2 7 4 .0 0

______PERCENT COHEOSlTiON______RADIUS INTERFASCICULAR FASCICULAR {mm) RAY TRACHEID RAY

30.0 4 63 33 2 9 .0 6 49 45 23.0 7 54 39 27 .0 7 59 34 2 3 .0 10 57 33 21.5 16 55 29 19.5 49 33 18 19.0 60 27 13 223

fa ille 22

Developmental Data

1U communis stem #7051 p rim ary xylem radius •= 9. 8 mm secondary xylem radius = 24.8 mm

TRACHEID FASCICULAR RAY RADIUS NUMBER LEN GTE DIAMETER NUMBER LENGTH DIAMETER 1mm) { c e lls ) (mm) (mm) {x 1000) (EH) (mm)

19.5 220 8 .1 * 1 .2 o 04 H . 009 8.0 .1 01*.024 .0 524.0 1 19.3 217 8.1 *1. 1 .0 4 1 4 .0 1 1 8o 2 . 102 4. 035 .0524.01'- 18.3 233 7.6 £1 .3 .0 3 8 * .0 1 0 7 .8 . 102^.029 .050*.01'< 17.8 212 7.9*1.2 .039*.010 8.1 . 1 03 f. 03 7 a 0504.0 1 1 6 .8 2 03 7 .4 * 1 .3 .0 4 1 * .0 0 9 7 .5 . 1024.031 .0 4 7 4 .0 0 15. 8 189 7 .4 * 1 .4 .0 4 0 * .0 1 2 6 .7 .1 1 1 * .0 2 8 .0464.00V 14 .8 160 7.3*1.3 .043 *.011 5.9 .1 2 3 4 .0 3 5 .0 4 7 * .0 1 . 12.8 161 6 .5 * 1 . 1 .0 4 1 4 .0 1 0 4 .0 .1 3 5 * .0 3 5 .0 4 3 * .0 0 11.8 159 5 .5 * 0 .6 .0414.013 2.4 „157*.042 .0 4 0 t.0 0 :

_&mCE132_£QJ3 PGJ5I1XQ N RADIUS INTERFASCICULAR FASCICULAR (mm) RAY TRACHEID RA X

19.5 6 59 35 19.3 6 59 35 18.3 6 59 35 17.8 6 59 35 16.8 7 59 34 15.8 9 56 35 14.8 9 55 36 12.8 18 53 29 11.8 30 49 21 224

Table 23

Developmental Data km communis stem #8576 p rim ary xylem radius = 18 .6 mm secondary xylem radius = 3 1 .5 mm

TRACHEID FASCICULAR RAY BADIUS NUMBER LENGTH DIAMETER NUMBER LENGTH DIAMETER (mmj ( c e lls ) (mm) (mo) (x 1000) (mm) (EE)

29.6 355 7.3 & 1.4 .0401.008 10.8 .1 1 1 1 .0 3 3 . 0 54*.0 1 2 5 .6 332 6.6*1.0 .0411.008 8.9 »110i«033 .0551.00 23. 1 3 05 6 .4 * 0 .7 .0 4 2 1 .0 0 7 6 .2 .1 3 3 * .0 3 0 .0 5 5 1 .0 0 22 .6 341 6 -1 * 0 .9 .0401.009 6.4 .139*.046 .0471.00 21 .6 335 6 .0 * 1 .3 . 04 11 . 007 5 .8 .1 4 1 * .0 4 1 .0 4 4 * .0 1 21. 1 307 5 .9 * 0 .9 .0391.008 5.9 .1571.059 .0421.00 20.6 291 5 .8 * 0 .9 .0 4 1 * .0 1 0 5 .0 .135*.043 .0401.00 20. 1 217 5 .7 * 0 .7 .040*.009 3.8 .1 5 9 1 .0 4 3 .0 3 9 1 .0 0 19.6 194 5 .0 * 0 .8 .0 3 8 * . 007 3 .5 .1 6 2 1 -0 6 5 .0 3 5 1 .0 0 19. 1 211 4 .6 * 0 .9 .0 3 1 * .0 0 6 2 .4 .235*®075 .0281.00 18.8 205 4 .3 * 0 .9 .0 3 1 *.005 1.8 .2 9 8 * . 107 .0 2 8 1 .0 0

______PERCENT COMPOSITION______RADIOS INTERFASCICULAR FASCICULAR (mm) BAY THACHEID______BAY

2 9 .6 9 56 35 2 5 .6 11 56 33 23.1 12 56 32 2 2 .6 12 59 29 2 1 .6 13 61 26 21. 1 17 53 30 2 0 .6 26 53 21 20. 1 42 39 19 19.6 54 30 16 19. 1 62 25 13 18.6 64 23 13 cliap& er I u m o i i i

T a b le 24

Developmental Data

A. d e i t o i d e s #209 B radius primary xylem = 0o 5 mm radius secondary xylem = 3.8 ms

TRACHEID______FASCICULAR RAY RADIUS NUflBER LENGTH WIDTH RUBBER LENGTH WIDTH (mm) ( c e lls ) (■fl) (mm) ( c e l l s ) (mm) (mm) \ 3 .5 9 .9 15.1 . 0941. 014 880 .0604.020 -036t .012 3 .2 10.8 13.8 .094±.016 775 .0594.020 .0354.009 2.7 10.3 13-1 .0944.013 442 .0674.022 .027 4.009 2 .2 10.1 12.2 .0894.015 344 .0674.030 .0264.005 1.7 10.7 9-8 .08 5 4 -0 1 8 278 .0724.021 .0254.006 1 .0 11.2 7.2 .0634.012 231 .0664.038 .0214.004 0 .9 12.0 6-3 .0584.0 07 195 .1004.053 .0224.009

XNTERFASCICOLAR ______PERCENT COMPOSITION « RAY CELL JFASCICULAR INTERFASCICULAR RADIUS LENGTH WIDTH BAY TBACHEID HAY (mm) (mm) (mm) (%) [%) i%)

3 .5 .134.05 .0604.018 27 64 9 3-2 . 124- 02 .0 6 3 4 .0 1 6 22 70 8 2 .7 .1 4 4 .0 6 .0 4 6 4 .0 0 8 20 75 5 2. 2 - 174.05 .0 2 7 4 -0 0 9 17 79 4 1.7 .1 9 4 .0 5 .0 1 8 4 .0 0 6 12 83 5 1-0 .2 5 4 .0 7 .0214.008 14 81 5 0 .9 .2 3 1 . 1 0 • 0 18 ±. 0 0 3 16 77 7

- 225 - 226

T able 25

Develocmeatal D ata is. deitoides #209 C

radius primary xylem = 0.7 mm

radius secondary xylem = 3.1 is

TRACHEID______FASCICULAR BAY AD I US NUflBER LENGTH WIDTH NUflBER LENGTH WIDTH (ms) ( c e lls ) ( be) (mm) ( c e lls ) (h ) (mm)

0 .9 9.3 6.7 .069t.O12 313 .0674.027 .0204.008 1o 1 8 .0 7.0 .086$.017 250 .0621.021 .0204.008 1.4 9 .3 7.9 .0804.011 338 .0581.023 — 026i .0 07 1.5 12-1 8.6 . 076i.013 260 .0741.065 „ 0 2 6 t.008 1.7 8.5 8.8 .0894.017 349 .0634.033 .0 3 0 1 .0 1 0 1.8 9- 0 9.0 „090±» 014 388 .0561.023 .0 2 9 1 .0 0 9 1.9 11.7 9.0 .0884.013 141 .0821.047 .0 3 0 1 .0 0 6 2. 3 10.6 10.1 .0 8 9 4 .0 1 1 702 .0581.025 .0 2 9 1 .0 0 9 2 .3 10.9 10.7 .085±. 014 692 .0751.030 .0 3 1 1 .0 0 9

INTERFASCICULAR ______PERCENT COMPOSITION RAY CELL FASCICULAR INTERFASCICULAR RADIUS LEN GTH WIDTH RAY TRACHEID RAY (mm) (mm) (mm) (5?) (55) (*)

0 .9 „1 8 1 .0 4 .0 1 4 1 .0 0 8 18 75 1 1.1 .141.03 .03 01.007 26 69 5 1. 4 . 131.03 .0 3 8 1 —010 27 67 6 1.5 . 2 0 t . 05 .0 1 7 1 .0 0 6 11 84 5 1.7 . 12f.03.0551.014 32 62 6 1.8 .131.02 .0621.014 30 64 6 1.9 .1 5 1 .0 4 - 0321.C09 19 78 3 2.3 . 10i.02 .0 6 9 1 .0 1 4 26 66 8 2. 3 . 121.03 .0 5 1±—013 21 68 11 227

fable 26

Developmental Data

A- deltoides #1808 radius primary xylem =■ 0-7 mm r a d iu s se c o n d a ry xylem = 3-5 mm

TRACHEID FASCICULAR RAY RADIUS NUMBER LENGIH HIDTH NUMBER LENGTH HIDTH (am) ( c e lls ) (mm) (ms) (cells) (am) (mo)

3-0 10-1 13-9 „095±-016 1290 -069±-021 -.0361-009 2-8 11-0 13,6 - 085 4-013 1000 -0601-019 -035#® COS 2-4 12- 1 12-6 -0771-010 620 -0544-018 -0271-006 1-9 9-6 12-2 -0771-011 370 - 0661.024 -0291-006 1-6 9-7 12-1 -0641-011 330 -055#-024 -.0221-005 1-4 9-3 11-2 - 062t. 009 210 -0611-024 .0 2 3 1 .0 0 5 1-0 8-2 9,6 -0551-008 200 -0731-033 .0 2 0 1 .0 0 3

INTERFASCICULAR ______E EBCENT COMPOSITION RAY CELL FASCICULAR IN1ERFASCICULAB RADIUS LENGTH HXDTH BAY TBACHEID RAY (mm) (mm) (mi) (55) {%) {%)

3,0 .111.04 .0481.017 16 71 12 2,8 . 121.03 .0391.007 16 72 11 2-4 - 11 i. 03 .0 3 7 1 .0 1 1 17 77 6 1.9 .111.02 .0361,009 18 76 6 1.6 .1 5 1 ,0 3 -0 2 8 4 .0 1 1 21 75 4 1.4 .2 3 1 .0 5 .0251.012 23 74 3 1.0 ,2 8 1 .0 6 .0221-007 27 68 5 C hapter I I afSEiiix s

T able 27

Developmental Data

Ho noei #371 radius primary body = 2-0 me radius secondary xylem = 17.0 mm

PERCENT TRACHEID COMPOSITION RADIOS NOMBER LENGTH WIDTH RAY TRACHEID (mm) ( c e lls ) ( mm) (BIB) 1%) {%)

5 0 2 14.9 20.2 . 108+.029 18 82 6. 3 13.2 2C.8 .119*.02 1 19 81 7.3 1 2 .0 22.9 .1 2 1 * . 0 27 19 81 8 .3 11.2 24.1 .128*.030 18 82 9.3 1 1 .6 23.8 . 140 *. 032 10 90

- 228 - 229

Table 28

Developmental Data

Eg, noei #678 radios primary body = 0.4 mm radius secondary xylem = 10.1 mm

PERCENT TRACHEID COMPOSITION RADIUS NUMBER LENGTH HIDTH RAX TRACHEID (mo) ( c e lls ) (mm) (mm) (%) (%)

9 .8 12.1 18.7 .0 9 7 4.021 3 97 9.1 9 .3 19.9 . 109 4.018 5 95 8 .5 9 .2 19.4 .1 0 9 4 .0 2 4 3 97 8.2 10.3 17. 1 .1054.023 4 96 7 .6 8a 2 2 2 .4 .0964.021 3 97 7 .0 7 .7 2 0 .6 . 1034.020 3 97 6 .3 7 .3 19.3 .1054.023 4 96 5.7 7 .6 18.4 .0964.016 5 95 5. 1 6.6 17.4 .1 0 5 4 .0 1 6 7 93 4.5 5 .9 * 17.9 . 109 4.022 3 97 3 .8 5 .5 16.4 .1 1 1 4 .0 2 6 6 94 2 .9 3.0 24.5 . 1 164.028 6 94 2-1 2 .9 2 2 .3 .1 2 3 4 .0 3 8 3 97 1.6 3 .5 16.3 . 1254.028 4 96 1.0 3.3 17.2 .110i.022 8 92 230

TaMe 29

Developmental Data

M® noei #831 radius primary tody = 2=1 mo radios secondary xylem = 14®1 mm

PERCENT TRACHEID COMPOSITION RADIUS NUMBER LENGTH WIDTH SAY TBACHE (mm) ( c e lls ) ( mm) ( ll ) {%) (?)

3®9 6 -7 22® 3 , 1891®038 21 79 4® 8 6® 7 23®4 ® 1854-® 040 21 79 5® 7 5®8 25, 1 ® 20 1J:® 045 23 77 7® 1 5®3 27®2 ®190i® 04 7 31 69 8® 0 6® 5 28-0 . 154 *® 030 32 68 8® 9 7® 1 25® 1 ®166&®035 25 75 1 0®3 9® 3 24® 3 ®169f® 040 15 85 11® 2 9® 8 2 4 ,9 ®162&-043 15 85 12® 1 9®3 24® 3 ® 158 i® 038 26 74 231

Table 30

Develocmenla1 Data

£& Hogi #€61 radius primary body = 2.8 mm r a d i u s se c o n d a ry xylem = 17=8 n

PERCENT THACHEID COMPOSITION RADIOS NUMBER LENGTH 0JD1H RAY THACHEID (ms) ( c e lls ) (mm) (mm) (?) (1)

6 .3 9 .9 2 2 .4 .1 7 0 * .0 3 6 27 73 7 .3 10.6 2 2 .0 „ 160 •£.0 22 30 70 8. 3 10.7 22.6 .1501.030 34 66 9.3 12.0 20.9 . 1541. 030 32 68 10.3 13. 1 2 2.2 .1 5 5 1 -0 3 0 23 77 11.3 14.0 22.0 . 1551.028 21 79 12. 3 15.7 22-4 .1 4 0 1 .0 2 8 21 79 13.3 14.4 2 4 .1 . 1421.029 15 85 14.3 13.9 25. 1 -1581-032 17 83 15.3 13.4 26.1 „ 1551.030 21 79 16.3 13- 1 26.7 -1541-024 24 76 17.3 15.2 27.5 . 1321.032 24 76 232

T able 31

Sevelopmental Data

Is. fioei #1239

radius primary body = 0,9 ma

radios secondary xylem = 8-0 mm

PESCEBT TBACHEXD COaPOSITlOM B1DIUS NUflBEB LEHGTH lilDSfl BAX TFACHEID {mm) { c e lls ) {mm) {mm) (%) (%}

7 .6 8 .7 2 6 .9 -1 384-023 20 80 7.1 8 .6 26.4 . 143s-. 023 19 81 6 .6 9.1 26. 1 .1431.027 14 86 6.1 8 .8 25.5 . 149 t . 027 16 84 5 .6 7 .9 25.9 . 1471.022 22 78 5.1 8.2 2 4.7 .1491.025 21 79 4 .6 8 .5 24.2 .1 4 9 4 .0 2 6 30 70 4.1 6 .9 23.8 . 1311.02 1 43 57 3 .6 5.3 27.0 .1311.021 50 50 3.1 5-4 27.5 . 128 1.017 49 51 2 .6 5 .9 27. 1 . 1 3 3 l . 032 43 57 2.1 5 .7 27.4 . 1381.03 1 42 58 1.6 6 .3 26.4 . 1321-023 40 60 Ctaagtec III

MSW11011 S

T ab le 32

Data— Cor daites

Gordaixyloa sp» #930 priaary xylem radius = 2-9 be secoadary xylem radius = 5*0 ma

PERCENT COMPOSITION TRACHEID ADI US RAY TRACHEID NUMBER LENGTH HIDTH (ma) (*) (?) ( c e l l s ) (Dm) (mm)

3 .4 5 95 161 3 - 6 tO-7 „033±»Q04 3*5 5 95 153 3 -9 t 0.5 »035t»005 3-6 4 96 159 3-9&0-7 . 037 J-- 004 3-7 4 96 163 3 «9f1-2 -035±« 005 3-8 4 96 205 3-240-8 -0 3 5 4 .0 0 6 3-9 3 97 206 3-3&0-8 -0354.006 4 .0 3 97 225 3- 1t0.8 .0341® 005

SECONDARY RAY RADIUS LENGTH HIDTH NUMBER (am) (mm) (mm) ( c e lls )

3-4 -040f®008 -0214-004 1300 3- 5 » 045j> 007 -0214-004 1200 3 — 6 -0404-008 -0201-003 1100 3 -7 - 0394.008 -0194-004 1200 3 -8 - 0411 - 009 -0214-003 1200 3-9 .0 4 1 * .0 0 7 -0191-003 900 4-0 -03 6 4®007 -0194-003 1200

- 233 - Table 33

Developmental Data flesoxvlon sp. #1014 primary xylea radius = 4-5 am secondary xylea radius = 12.4 ms

PEBCENT COMPOSITION TBACHEXD ADI as RAX TRACBEXD NUMBER LENGTH 1IDIH (mm) {*) (%) ( c e lls ) (ms) (mm)

4-5 29 71 258 2- 1*0-7 . 03 0 ± -006 5. 1 10 90 300 2.6* 0-6 -0 3 1 ± . 005 5.6 9 91 279 3.1±0-8 .036*.006 6. 1 9 91 255 3 .7 4 0 .9 »036t= 007 6 ,5 6 94 288 3.6*1.4 .0 3 5 * .0 0 5 7. 1 6 94 276 4.111.0 .0 3 9 * .0 0 6 7-8 8 92 290 4-241- 1 «Q37±.0Q7 8a 3 8 92 302 4-341-0 -0404-008 8-3 8 92 366 3-8*1- 1 .0 4 0 4 -0 0 9 9-4 9 91 372 3 .9 M .2 .038#-.006 9-9 7 93 364 4 . 3 *1- 3 .0 3 6 4 .0 0 7 10-5 9 91 396 4.141.3 .0 3 8 4 .0 0 6 11.0 10 90 410 4 . 141.2 .0 4 3 * .0 0 8 1 1a 6 9 91 498 3 .6 * 1 -0 -036*-007 12-0 9 91 562 3 -3 * 0 .9 »Q 39±.010

SECONDARY RAY RADIUS LENGTH HIDTH NUMEEB (mm) (mm) (mm) ( c e lls )

4.5 -0404-010 -0254.006 10600 5- 1 - 0 2 9 * -C10 -0144-003 10600 5.6 -0274.010 .0134.003 11900 6- 1 -027t.008 -0154.004 11600 6 .5 -0324-007 -0164-003 7200 7. 1 -0334-010 -0164.004 1 COO 7.8 -0314-008 .0 1 8 4 .0 0 4 9000 8- 3 -0344-008 .0181.004 8900 8.9 -03H.007 .0 1 6 4 .0 0 4 11500 9-4 -0334-009 .0194-004 11300 9.9 -0374.009 -0184-005 8300 10-5 -0374-016 -0204-005 10900 11-0 .0 3 9 * .0 1 7 . 022 4- 005 11100 11-6 -0 3 5 4 .0 1 0 -0204-005 12300 12-0 .0384.017 -022 4-004 11000 T able 34

Developmental Data

Cordaixylon sp. #1190 primary xylem radius = 7.0 mm secondary xylea radius = 9.9 mm

PE1CENT COMPOSITION ______TR&CHEID ADI US BAY T MCE BID MHBIB LENGTH WIDTH (mra) (35) (55) ( c e lls ) (mm) (mm)

7.1 4 96 503 3 .0 * 1 .0 .0 2 8 4 .0 0 7 7 .2 3 97 488 3 .0 4 0 .9 .0 3 0 4 .0 0 5 7 .4 3 97 420 3 .7 *0.7 .0 2 9 4 .0 0 7 7 .6 3 97 326 4 .3 4 0 .9 .0 3 3 4 .0 1 0 7 .7 3 97 309 4 . 6 1 0 .9 .0 3 3 4 .0 0 9 8. 1 3 97 307 4.6* 0.8 .03 5 *.007 8 .3 3 97 343 4 .1 * 0 .8 .0 3 6 4 .0 0 8 8 .6 3 312 4 .8 * 0 .9 .0 3 5 4 .0 0 5 8 .9 3 97 369 4 .2 4 0 .9 .0 3 5 4 .0 0 9 9 . 2 2 98 315 5 .0 4 1 .0 .0 3 6 4 .0 0 8 9 .4 3 97 310 5 .0 * 0 .7 .0 3 7 4 .0 1 0 9 .6 3 97 363 4.6* 0.9 .0 3 5 4 .0 0 6

SECONDARY RAY ADI US LEN GTH WIDTH N UNBED (mm) (mm) (mm) ( c e lls )

7. 1 .C39S-. 014 .0141.003 4420 7 .2 .040t= 014 .0 1 3 f.0 0 2 3470 7 .4 . 0 3 6 4»«C10 . 0 1 4±.C03 360 0 7 .6 .034#-..022 .0 1 3 4 ,0 0 2 4580 7 .7 .0 3 4 * . 012 .0 1 4 4 .0 0 3 4100 8.1 .0 2 9 * . 008 .0 1 3 4 .0 0 2 5180 8 .3 . 0321«»009 .0 1 5 4 .0 0 3 4290 8 .6 .0 2 9 t . 007 . 0 1 5 ± .003 5000 8 .9 .0 3 6f«007 .0 1 5 4 .0 0 3 4160 9 .2 . 02.9t. 006 .0 1 4 4 .0 0 3 3690 9 .4 . 036 i.»020 .0154.003 4590 9 .6 .0 3 7 t . 010 .0 1 5 4 .0 0 3 4330 T ab le 35

Developmental Data

Cordaixvlon sp. #1500 primary xylem radius = 4. 3 am secondary xylem radius = 8-2 mm

PERCENT COMPOSITION TRACHEID ADI as BAY TRACHEID KOHBEfi LENGTH HIETH (mm) (*) {*> ( c e l l s ) (mm) (mm)

7 .3 4 96 291 4 .2 6 0 .9 .0 3 9 ± .0 0 6 7. 2 4 96 323 3 . 7 t 0.7 » 036&.006 7.1 4 96 330 3 .6 f 0 .6 -0 3 6 i.0 0 5 6™ 9 4 96 312 3.7± 0.7 „035±.004 6 .7 4 96 281 4. 011.0 .036±.005 6. 5 6 94 281 3,8±0„4 .0361-006 6.3 4 96 229 4 . 6 t 0 . 7 . 035±.004 6. 1 5 95 241 4.2& 1.0 . 036±.004 5 .8 4 96 216 4.5±0.8 .035±.008 5 .4 4 96 251 3.6& 0.7 .0 3 7 6 .0 0 5 5.1 6 94 261 3 .2 ± 0 .7 .0 3 4 1 .0 0 7

SECONDARY RAY RADIUS LENGTH 8IDTH BUHEEB (mm) (mm) (mm) ( c e l l s )

7 .3 „0 2 7 ± .008 .0 1 2 1 .0 0 3 7 520 7 .2 .0 2 8 1 .0 0 7 .0 1 3 + .0 0 3 7990 7.1 .0 3 0 1 .0 1 6 .0 1 3 1 .0 0 3 5660 6.9 .0291.007 .0 1 3 1 .0 0 3 622 0 6.7 .0291.013 .0 1 2 1 .0 0 3 6400 6.5 .0291.006 .0161-003 7140 6.3 .0281.011 .0 1 3 1 .0 0 2 5740 6.1 .0311.011 ,013±.002 6220 5.8 .0301.013 .0141.003 4920 5 .4 .0 2 6 6 . 014 .0 1 3 1 ,0 0 3 5360 5.1 .0 3 1 1® 014 .0 1 6 1 .0 0 3 5340 S ab le 36

Developmental Data

CordairyIon sp. #4507 primary xylem radius = 16-0 mm secondary xylem radius - 34®1 mm

PEBCENI COHPOSITION ______TRACHEID RADIUS SAY TRACHEID N0HBE1 LENGTH IIDTH (mm) 1%) (%) (cells) ffiB) (mm)

3 4 .0 6 94 1905 3.4&Q.9 -031*. 006 33® 5 5 95 1443 4 -2 4 0 .9 .0 3 3 4 .0 0 4 33»2 5 95 1019 5 .4 * 1 .4 .0 3 6 4 .0 0 9 32-7 4 96 1034 5.3*1.3 .0 3 6 4 .0 0 5 32«2 4 96 991 5 .6 * 1 .0 -0 3 5 1 .0 0 6 31-7 4 96 1023 5 .5 * 1 .2 .0 3 4 4 .0 0 6 31.3 4 96 865 5 .9 * 1 .0 .0 3 7 1 .0 0 8 30c. 6 4 96 964 5.811.4 .0334.006 30-2 4 96 913 5 .7 * 0 .9 .0 3 5 4 .0 0 6 29-7 4 96 835 5 .8 1 1 .3 .0 3 7 4 .0 0 6 2 9 .3 3 97 870 5.7 * 1. 5 -0 3 6 1 .0 0 6 28.7 4 96 740 6.0*1.2 .0394.005 28-1 3 97 755 6.3*1. 1 .0364.005 27 .6 3 97 685 6 .3 * 1 .2 .0 3 9 4 .0 0 6 26-8 3 97 803 5. 5* 1.4 .0 3 7 * .0 0 6

SECONDARY RAY RADIUS LENGTH WIDTH NUMEER {mm) (mm) (mm) ( c e lls )

3 4 .0 -0374-010 -0174.004 26600 33- 5 .036f » 010 .0161.003 23500 33-2 -034*.010 .0174.004 25000 3 2 .7 .0 3 5 * .CO 9 .0 1 6 4 .0 0 2 19800 3 2 .2 .0 3 2 1 .0 0 7 .0 1 5 4 .0 0 3 22900 31.7 .0344.020 .0 1 4 4 .0 0 3 22500 31.3 .0304.008 .0144.003 24800 3 0 .6 .0 3 4 4 .0 0 8 .0 1 7 4 .0 0 3 17800 30-2 .0 3 6 4 .0 0 7 .0 1 6 4 .0 0 3 17900 29.7 .0324.010 - C171.004 18500 29 .3 .0281-009 -0141-003 17900 28.7 .0304.006 .0151.002 21300 28.1 ,0 3 1 4 .0 0 8 -0 1 5 1 .0 0 3 14200 2 7 .6 .0 2 9 4 .0 0 7 .G14+.C02 16900 2 6 .8 -0301.006 .0141.002 15700