Studies of Paleozoic Seed Ferns: Anatomy and Morphology of Morphology of Microspermopteris Aphyllum

Amer. J. Bot. 63(10): 1302-1310. 1976.

STUDIES OF PALEOZOIC SEED FERNS: ANATOMY AND MORPHOLOGY OF MICROSPERMOPTERIS APHYLLUM1

THOMAS N. TAYLOR AND RUTH A. STOCKEY Departmentof Botany,The Ohio State University,Columbus 43210

A B S T R A C T The discoveryof numerousspecimens of the monostelicpteridosperm genus Microspermop- teris in Pennsylvaniancoal ball petrifactionsfrom the Lewis Creek and What Cheer localities providesadditional information about the anatomicaland morphologicalvariability within thegenus. Specimensare now knownup to 1.1 cm in diam thatbear epidermalappendages in theform of variously-shapedtrichomes. The externalsurface of the stemis furtherornamented by longitudinalflaps of corticaltissue. Petiolesexhibiting a singleC-shaped vascular strand with abaxial protoxylemare producedin a 2/5 phyllotaxy.Large petiole bases that clasp the stemproduce primary pinnae alternately. The presenceof axillarybranching appears similar to thatreported in Callistophytonand Lyginopteris. Triarchto polyarchadventitious roots, some withsecondary tissues, are producedat both nodal and internodalregions. Of the cur- rentlyrecognized monostelic seed ferngenera, Microspermopteris is most similarto Heter- angium. Informationis presentedthat supportscurrent ideas regardingthe evolutionof the gymnospermiceustele from protostelic Devonian ancestors.

THE GENUS MICROSPERMOPTERISwas initiallyde- axes representingnumerous orders of branching. scribedby Baxter (1949) frompetrifaction ma- Specimens were collected fromthe What Cheer terial collected fromthe What Cheer locality of and Lewis Creek petrifactionlocalities which Iowa, witha subsequentvariety added fromma- are designatedMiddle and Early Pennsylvanian, terialcollected from the FlemingCoal of Kansas respectively (Good, 1975). Cellulose acetate (Baxter, 1952). Recently,the taxon has been peels were used to determineanatomical and reportedfrom several coals in Illinois (Mahaffy, morphologicalfeatures. All specimensand slides 1975) and easternKentucky (Taylor and Stoc- are housed in the PaleobotanicalCollections, De- key, 1975). In the initialdescription the genus partmentof Botany, The Ohio State University, was characterizedas a leaflesspteridosperm with and include acquisition numbers 6,489-6,912, an exarch, partiallymixed protosteleup to 5.0 12,177-12,420, 12,422-12,466. mm in diam. Stems were describedas being irregularin outlineand lackingleaves. Multicellu- DIAGNOSIs-Microspermopterisaphyllum (Bax- lar emergencestogether with adventitiousroots ter) Taylor et Stockey emend. Stems up to 1.1 were described on some stem fragments.The cm in diam withmixed exarchprotostele consist- genus was furthercharacterized by the presence ing of large metaxylemtracheids and up, to 10 of secondary tissues, concentricbranch traces, peripherallypositioned protoxylem strands. Pet- and distichousbranching. ioles arranged in 2/5 phyllotaxy,with single Duringthe past severalyears we have accumu- trace slightlyC-shaped with abaxial protoxylem; lated a numberof specimensof this plant from petiole base large and clasping up to one half two petrifactionlocalities in North America, stem circumference,primary pinnae produced especially the Lewis Creek site in eastern Ken- alternately;axillary branches with abundant sec- tuckywhere it representsa common elementof ondaryxylem. Cortex of thin-walledparenchyma the flora. It is our intentin this paper to provide with secretorycells in youngerstems, and pe- additional informationabout this taxon, offera ripherally disposed longitudinal sclerenchyma; reinterpretationof severalmorphological features, peridermof thick-walledradially aligned cells. and discuss the genus Microspermopterisin light Stem surface ornamentedby longitudinalflaps of recenttheories regarding the evolutionof the of corticaltissue, and multicellular,typically flat- gymnospermoushabit. tened trichomes. Metaxylemtracheids elongate, The followingdescription is based upon 36 with multiseriatebordered pits; protoxylemele- mentsscalariform. Primary xylem pentagonal in 'Received for publication17 December 1975. cross section and divided into 5 sectionsby lon- The authorsare indebtedto Dr. John W. Hall for gitudinal parenchymaplates that radiate from making several What Cheer specimensavailable for study,and to the National Science Foundationfor par- stem center; protoxylemstrands occur in pairs, tial supportof this research(BMS74-21105). one strandon each side of a parenchymaplate. 1302 November-December,1976] TAYLOR AND STOCKEY-MORPHOLOGY OF MICROSPERMOPTERIS 1303

Secondary vascular tissues well-developed,sec- trace has been formedit remainswithin the stem ondaryxylem tracheids with uni- and multiseriate cortexfor some distance(approximately 6.0 mm) bordered pits. Xylem rays up to 2 cells wide. beforepassing outwardinto the petiole base. Triarchto polyarchadventitious roots, some with The most conspicuousaspect of the cross sec- secondarytissues, arising at both nodal and inter- tional configurationof Microspermopterisis the nodal regions. presence of large, angular metaxylemtracheids (Fig. 1). In longitudinalsection, metaxylem ele- Type species- Microspermopterisaphyllum mentsmeasure up to 1.0 mm and possess slightly Baxter 1949, p. 297-298, pl. 2, Fig. 1-4; pl. 3, tapered end walls, and multiseriate,simple-retic- Fig. 5-7; pl. 4, Fig. 8-12. ulate-borderedpits (Fig. 19). Parenchymain the metaxylemis organized into longitudinalplates Synonymy-1952. Microspermopterisaphyl- up to threecells wide thatradiate from the center lum var. kansensisBaxter; Trans. Kansas Acad. of the stem to formthe characteristicpentagonal Sci. 55: 101-103. stem configuration(Fig. 4). We have observed a largernumber of plates in some stems;however, DESCRIPTION-General features-Stems range in all instancesthis increase in numberof plates from0.5-11.0 mm in diam, with the most com- appears to have resultedfrom additional divisions plete specimenextending approximately 38.0 cm of the originalfive plates (Fig. 1). through the coal ball. Most stems exhibit a sinuous habit in the matrixmaking longitudinal Axillary branching-One of the newly inter- stem sectionsdifficult to obtain and possiblyre- pretedfeatures of Microspermopterisis the pres- flectinga liana or shrub-likegrowth habit. A ence of axillarybranching (Fig. 24). Figures 12- pentagonal protostele containing longitudinal 14, 17-18 illustrateprogressive stages of stem plates of parenchyma (Fig. 1, 4, 15) is sur- and petioleseparation, and axillarybranch origin. rounded by a well-developedzone of secondary The productionof an axillarybranch begins with xylem. To the outsideof this tissueis a vascular a large amount of secondary xylem extending cambium, a zone of secondary phloem, and a laterallyfrom the stem stele (Fig. 13). At a parenchymatouscortex containing patches of slightlyhigher level (Fig. 12, 14) it becomes sclerenchymaand secretorycells (Fig. 1, 4, 7, separated to form a tereteaxillary branch stele. 11, 16). Multicellulartrichomes and longitudinal Figure 17 representsthe axillarybranch, traced corticalflaps extendfrom the stem surface (Fig. for a distanceof approximately5.3 mm. In this 2, 5, 8, 9, 25). specimenthe more distal organizationof the axillary branch could not be determinedbecause of Primarytissues-In transversesection the pri- faultypreservation. In tranversesection the axil- maryxylem is typicallypentagonal in outline as lary branch stele is circularwith a centralregion definedby radiatingparenchyma plates (Fig. 1, of small crushedcells possiblyrepresenting proto- 4). At the moredistal levels of the stemthis con- xylemelements or parenchyma,surrounded by a figurationis maintainedby clustersof metaxylem zone of up to 12 rows of secondaryxylem tra- tracheids separated by patches of parenchyma cheids. At the point of axillary branch origin (Fig. 7). In the stemthat contains the most sec- there is a distinctinterruption in the secondary ondary xylem (Fig. 4) (Lewis Creek) the pri- xylem of the stem stele (Fig. 17, 18, arrows). maryxylem measures 1.1 mm in cross sectional At higherlevels a few files of secondaryxylem diam,whereas the stemillustrated in Fig. 1 (What tracheidsare present. Cheer) has approximatelyone-third the secondary tissue developmentand the primaryxylem is Petiole-The petiole or rachis clasps the stem 1.7 mm in diam. The stem illustratedin Fig. 7 axis for approximatelyone half of the diameter is representedalmost entirelyby primarytissues. of the stem at the level of axillarybranch forma- The protoxylem strands in Microspermop- tion (Fig. 12, 24). At higherlevels the cross teris, as determinedby cell diameterand pres- sectionalconfiguration of the petiole is V-shaped ence of annular-scalariformwall thickenings,are to almost flattened (Fig. 17, 21). In several situatedon eitherside of the parenchymaplates specimens it has been possible to trace alter- that radiate fromthe stem center (Fig. 3). Fig- natelyarranged primary pinna axes (Fig. 20-22). ures 3, 6, and 10 illustratesuccessively higher The pinna trace consists of a single lateral xy- levels throughprotoxylem strands in a region of lary extension that shows the same anatomical organizationas the trace. Two trace petiole longitu- emission. In Fig. 3 the arrows on either dinal extensionsof tissue ornamentthe adaxial side of the metaxylemparenchyma indicate the surfaceof the petiolenear the level of pinna trace small protoxylemstrands. At a slightlyhigher formation(Fig. 21-22). It has not been pos- level (Fig. 12) the 2 strandsunite to form an sible to demonstrateconclusively more than a abaxial C-shaped bundle containinga circular single order of petiole branchingor the presence strand of large metaxylemtracheids. After the oflaminar pinnules. 1304 AMERICAN JOURNALOF BOTANY [Vol. 63

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Secondary tissues-In almost all of the stems Baxter (1949) in the initialwork on the genus, examined there is evidence of some secondary nor a zone of tangentiallyaligned scleroticcells. development.In older stems (Fig. 4) secondary Vertically aligned mucilage cells are scattered xylem consists of radially aligned tracheidsin- among the parenchymaof the cortex of some terspersedwith vascular rays. Wood segments stems (Fig. 7). The presence of these cells, as vary from1-4 cells wide withthe individualtra- well as the tangentiallyoriented sclerotic fibers, cheids square to rectangularin outline. Tracheids appears to depend upon the age of the stem,de- in the secondary xylem are approximatelyone gree of preservation,and level of section. In eighththe cross sectionaldiam of the metaxylem some stems a well-developedperiderm is present elements. Pittingis similarto that found on the withinthe cortex. It consists of up to several metaxylemtracheids. Bordered pits are also rows of radiallyaligned cells that probablycon- presenton the radial walls of secondaryxylem stitutethe phelloderm,and an outer,thinner zone tracheids,but typicallylack a regular arrange- of thick-walledcells of the phellem(Fig. 16). ment. Xylary rays are constructedof procum- Longitudinallateral extensionsof the cortex bent parenchymathat is organizedin both uni- give the more distal stems a wing-likeappear- seriate and biseriate files. A narrow, poorly ance (Fig. 2, 7, 23). These lateral extensions preservedcambial zone is presentto the outside lack a distinctmorphology and reflectthe irreg- of the secondaryxylem (Fig. 1, 16). ular outline of the cortex. In addition to these Small, rectangularsieve cells up to 25 /m in corticalflaps, there are irregularly-shapedmulti- diam and phloemparenchyma constitute the zone cellular trichomes(Fig. 5, 8, 9). They may be of secondary phloem (Fig. 11). The smaller sharplytapered (Fig. 9), or clusteredinto several phloem parenchymacells are organized in tan- finger-likeprojections that arise froma common, gential chains of 2-5 cells that alternatewith expanded base (Fig. 5). These structuresare largercells, presumedto be sieve elements. This presentat all levels of the stems (Fig. 25), but is similarto what has been describedin Callisto- appear to be more commonalong the distal parts phyton(Rothwell, 1975). In the stemillustrated of axes, and at nodes. These structuresdo, not in Fig. 11 this region is approximately0.3 mm appear to have been producedin any orderlyar- thick. Preservationdoes not allow for the posi- rangement. tive identificationof sieve areas. Phloem rays show some increase in widthtoward the periph- Roots-Triarch to polyarchadventitious roots, ery of the stem (Fig. 11). Parenchymaof the some showingwell developed secondarytissues phloemrays is identicalto the parenchymaof the are presentat all levels along the stems except platesin themetaxylem. on distal axes (Fig. 25). Roots are present at Several stemsshow distinctdifferences in sym- both nodal and internodallevels. Many branch metry(Fig. 4). This featureis quite noticeable and displaya sinuous course throughoutthe coal in relativelymature stems with extensivelyde- ball similar to that exhibited by small stems. veloped secondaryxylem, and appears to be the Older roots may be distinguishedfrom younger result of gaps formed in the secondary xylem stemswith small amountsof secondaryxylem by when branchesare produced (Fig. 4, 17, 18). the absence of radial parenchymaplates. Both exhibitprominent mucilage ducts in an irregularly Cortex-The cortexis irregularin outline and shapedcortex. is constructedof thin-walledcells. Toward the peripheryof the stem the corticalcells decrease DISCUSSION-There are a numberof so-called in diameterand possess slightlythicker walls. We monostelic seed ferns to which Microspermop- have not been able to distinguishwith any degree terismay be compared. These includethe genera of regularitythe two-partedcortex reportedby Stenomyelon,Lyginopteris, Callistophyton, Schop-

Fig. 1-10. Microspermopterisaphyllum. 1. Transversesection of stemshowing pentagonal primary body, well- developedsecondary xylem, and extraxylarytissues. Arrows indicatepositions of departingpetiole traces. C.B. 1298 B (1)1(2) #10. x 16. 2. Transversesection of stemshowing irregular outline and numerouscortical projections. C.B. 198A, #106. X 25. 3. Section showingformation of petiole trace. Arrowsindicate position of protoxylemelements. Larger cells representmetaxylem tracheids. C.B. 6057 C top, #123 ,B. X 95. 4. Trans- verse sectionof stem with well-developedsecondary xylem. Note pentagonalconfiguration of primarybody. C.B. 6057 C top, #123 3. X 16. 5. Transversesection of stem showingcortical projections. C.B. 198A, #106. X 100. 6. Formationof petioletrace at slightlyhigher level than that of Fig. 3. Arrowsindicate position of protoxylem tracheids.C.B. 1298 B(1)1(2), #5. X 95. 7. Transversesection of young axis showingsecretory cavities in cortexand irregularstem outline. Note small amountof secondaryxylem. C.B. 1061 B bot, #3. x 24. 8. Trans- verse sectionof multicellulartrichome. C.B. 198A side, #30. X 100. 9. Longitudinalsection of multicellular trichome.C.B. 198A side, #30. x 100. 10. Transversesection of petioletrace at slightlyhigher level thanFig. 6. Arrowsindicate the positionof protoxylemelements. C.B. 1298 B(1)1(2), #5. X 95. pp, parenchymaplate. 1306 AMERICAN JOURNALOF BOTANY [Vol. 63

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Fig. 20-22. Microspermopterisaphyllum. Successiveseries showing departure of primarypinnae. 20. Depart- ing pinna trace still within petiole cortex. C.B. 6057 C top, #91. X 17. 21. Higherlevel than Fig. 20 showing primarypinna almost separatedfrom petiole. Note the flattenedconfiguration of the pinna axis. C.B. 6057 C top, #123 P. X 47. 22. Still higherlevel showingpinna separatedfrom petiole, and initiationof new trace from oppositeside of petiole. C.B. 6057 C top. #146 ,p. X 17. Arrow in each figure depicts primary pinna axis from lower level. PT, petiole trace; PPT, primarypinna trace. fiastrum,Rhetinangium, Calamopitys, and Heter- from the Illinois Basin, while Andrews ( 1942) angium. Of these the genus Heterangiumshows detailed the stelar anatomyof a new species, H. the closest affinityto Microspermopteriswhen americanum. The recent study by Shadle and only featuresof the stele are considered. Stidd (1975) has expanded our knowledgeof the Specimens of Heterangiumare relativelyrare rachial anatomyand pinnule organizationof the in North American petrifactionmaterial. Gra- Heterangiumfrond. ham (1935), and Fisher and Noe (1938) re- Stems of Heterangiumextend up to 5.0 cm in ported the occurrenceof the genus in coal balls diam and are characterizedby irregularbranch-

Fig. 11-19. Microspermopterisaphyllum. 11. Transversesection showing extraxylary tissues. C.B. 1298 B(1)1(1) bot, #2. X 100. 12. Transversesection at level wherestem, axillary branch, and petioleare attached.Note inter- ruptionproduced in stemsecondary xylem near pointof branch departure.C.B. 198 B bot, #226. x 15. 13. Sectionof stembelow thatof Fig. 12 just afterpetiole trace departure.C.B. 198 B bot, #313. X 15. 14. Trans- verse sectionslightly higher than Fig. 12 in which petiolehas separatedfrom stem. Note claspingC-shaped configurationof petiole. C.B. 198 B bot, #205. X 15. 15. Radial sectionof metaxylemshowing longitudinal organiz- tion of parenchymaplate. C.B. 6000 I side, #214, x 110. 16. Transversesection of stemshowing periderm and sclerenchymaof cortex. C.B. 1298 B(1)I(2) #10. x 95. 17. Transversesection at level higherthan Fig. 14 with axillarybranch almost separated from stem. Axillarybranch stele is missing.C.B. 198 B bot, #157. x 15. 18. Transversesection considerably higher than Fig. 17 showingrelationship between stem and petiole. C.B. 198 B bot, #95. X 15. 19. Circular borderedpits of metaxylemtracheid. C.B. 198 A side, #47. x 180. AB, axillarybranch; P, periderm;PP, parenchymaplate; PR, phloemray; PT, petioletrace; S, stem;SC, sclerenchyma- tous cortex;SP, secondaryphloem. 63 1308 AMERICAN JOURNAL OF BOTANY [Vol.

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Fig. 23-25. Microspermopterisaphyllum. 23. Stem segment showing irregular outline of cortex and flattened epidermal trcoms 24. Segment of ste-m at nodep showingr rorign of axillarv branch. Note claspDingpetiole. 25. November-December,1976] TAYLOR AND STOCKEY-MORPHOLOGY OF MICROSPERMOPTERIS 1309

ing. The primarybody consists of a mixed, wherethere are also 5 axial bundles. In Micro- mesarch protostelein which the large tracheids spermopteris,however, the protoxylemstrands occur in clusters surrounded by parenchyma. occur on either side of the outer edges of the Secondaryxylem is producedin varyingamounts. metaxylemparenchyma plates, with each member Radially elongate bands of fibersare presentin of a pair arisingfrom a differentaxial bundle. In the outer cortex, while the inner cortex is de- S. tuedianum,traces are not positionednear the limitedby horizontalplates of thick-walledcells. parenchymaplates. In Stenomyelonthe presence One of the principaldifferences between the two of a cylindricalsystem of 5 sympodiais identical genera is the numberof tracesto the petiole. In to that described in Callistophyton(Rothwell, Microspermopterisone trace is present,while the 1975) and Lyginopteris;however, in Steno- frond of Heterangiumis vascularized by 2-10 myelon the basic protostele is maintained. strands depending upon the level of section Whetheror not the metaxylemwedges and asso- (Shadle and Stidd,1975). ciated protoxylemstrands of Microspermopteris Vascular rays of Heterangiumbroaden toward shouldbe regardedas sympodiacan not be stated the outside of the stem and may appear wedge- withcertainty at thistime. We have been able to shaped, while those of Microspermopterisremain follow the parenchymaplates for up to 3 cm. relativelyuniform throughout their extent. The Serial transversesections indicate that they remain mixed,mesarch protosteles of most Heterangium intact for a considerableextent throughout the axes usually contain more parenchymathan do stem; however,they do undergosome change in steles of Microspermopteris.The large meta- position. xylemtracheids of Heterangiumare more circu- In additionto the similarityof the sympodial lar in transversesection than those of Micro- systemin Microspermopteristo thatof some other spermopteris.Throughout the course of thisstudy monostelic seed ferns, the stelar organization we have noticeda small numberof stemsof Het- may be regarded as occupyingan intermediate erangiumfrom the Lewis Creek and Derringer position between some calamopityean axes of Corners localities that have primarybodies that Devonian age and youngereustelic Carboniferous resemblethe conditionseen in Microspermopteris forms,with referenceto the amount of paren- axes; i.e., the presence of 5 prominentlarge chyma. In a few stems,especially those fromthe wedgesof metaxylemtracheids and radiatingarms What Cheer site,we have observeda furtherdis- of parenchyma.A fewof theseHeterangium axes section of the metaxylemwedges by secondary have uniseriate-biseriaterays with just a few filesof parenchyma(Fig. 1). These parenchyma wedge-shaped vascular rays, but exhibit the plates, however, generallyarise at right angles typical petiole anatomy of Heterangium. Until to the principalmetaxylem plates. At some levels the reproductiveorgans are known for both Mi- the number of these secondaryplates increases crospermopterisand Heterangium,petiole anat- to the extentthat relatively small clustersof meta- omy will continueto be the distinguishingchar- xylem tracheids become surroundedby paren- acter. chyma. This organizationis quite similarto the Duringrecent years there has been an increased primary xylem organization of Heterangium. interestin the primarybody of vascular plants. Thus Microspermopterismay be added to a series This has been broughtabout principallythrough that demonstratesa conversionfrom the proto- the work of Beck and co-workers(Namboodiri stele to the eustele by an increasingmedullation and Beck, 1968 a, b, c) who have describedin of theprimary xylem cylinder. detail the primaryvasculature in a number of There are slight differencesbetween Micro- coniferophyticgymnosperms. Beck (1970) has spermopterisaxes from differentlocalities. For convincinglydemonstrated that the eustelicform example, stems from What Cheer typicallydis- like that of Lyginopterisor Callistophytonhas play larger primaryxylem cylindersand lesser evolved by longitudinaldissection of a protostele amountsof secondaryxylem than those of equiv- followedby modificationof columns of vascular alent size fromLewis Creek. The What Cheer tissue into discrete sympodial systemsarranged stemsshow a furtherdissection of the 5 primary in a cylinder.Beck has postulateda phylogenetic xylemsegments by additionalparenchyma plates series beginningwith a number of protostelic that extend at rightangles to the 5 main plates forms included withinthe Calamopityaceae be- (Fig. 1, 4). Whetherthis feature is a phylogenetic ginningwith species of Stenomyelonand Calamo- trend,since Lewis Creek fossils are Early Penn- pitysand extendingto Lyginopteris.Stenomyelon sylvanian and What Cheer, Middle Pennsylva- tuedianum (Kidston and Gwynne-Vaughan, nian, or merelya geographicalvariation, is not 1912) is interestingin thatit consistsof a proto- certain. stele divided into 3 longitudinalcolumns by Of additional interestis the presence of epi- radiatingbands of parenchyma.Despite thethree- dermaltrichomes and corticalflaps of tissue aris- angled appearance of this stem in transversesec- ing fromthe stemsof Microspermopteris.There tion, traces originatefrom 5 positions. This is are numerous Devonian genera that produced similarto the organizationin Microspermopteris epidermal appendages varyingfrom what have 1310 AMERICAN JOURNAL OF BIOTANY [Vol. 63 been described as spines to papillae (e.g., Cre- (Gaspe), and Ontario,Canada. Paleontogr.Amer. naticaulis (Banks & Davis, 1969), Kaulangio- 8: 77-127. phyton (Gensel, Kasper and Andrews, 1969), BAXTER,R. W. 1949. Some pteridospermstems and 1971), Pertica (Kasper and fructificationswith particular referenceto the Sawdonia (Hueber, Medullosae. Ann. Mo. Bot. Gard. 36: 287-352. Andrews, 1972), Psilophyton(Banks, Leclercq 1952. The coal age flora of Kansas. 1. Mi- and Hueber, 1975). Epidermalappendages have crospermopterisaphyllum var. kansensisvar. nov. been described on the stems of Callistophyton Trans. Kans. Acad. Sci. 55: 101-103. (Rothwell, 1975) and Lyginopteris(Oliver and BECK, C. B. 1970. The appearanceof gymnospermous Scott, 1904) in the formof glandulartrichome- structure. Biol. Rev. 45: 379-400. like emergences. As far as can be determined FISHER, M. C., AND A. C. Not. 1938. A list of coal fromthe literatureno othersupposed monostelic ball plantsfrom Calhoun, Richland County. Trans. seed ferngenera are known with epidermaltri- Ill. Acad. Sci. 31: 178-181. GENSEL, P., A. KASPER, AND H. N. ANDREWS. 1969. chomesor corticalflaps of tissue. It is of interest Kaulangiophyton,a new genus of plantsfrom the to notethat the surfaceof Stenomyelontuedianum Devonian of Maine. Bull. Torrey Bot. Club 96: is characterizedby epidermal emergencesthat 265-276. vary fromshort and bluntto elongateforms with GOOD, C. W. 1975. Pennsylvanian-agecalamitean swollenends. The authorssuggest that they may cones, elater-bearing spores, and associated vege- represent transverse sections of longitudinal tativeorgans. PalaeontographicaB, 153: 28-99. ridges of the stem (Kidston and Gwynne- GRAHAM,R. 1935. Pennsylvanianflora of Illinois as Vaughan,1912). revealedin coal balls. 2. Bot. Gaz. 97: 156-168. Microspermopterismay now be included with HUEBER, F. M. 1971. Sawdonia ornata: A new name for Psilophytonprinceps var. ornatum.Taxon 20: Callistophytonand Lyginopterisas examples of 641-642. monostelicseed fernsin which axillarybranch- KASPER, A. E., JR., AND H. N. ANDREWS, JR. 1972. ing is present. Rothwell(1975) has demonstrated Pertica a new genus of Devonian plants from the presence of axillary buds in Callistophyton northernMaine. Amer. J. Bot. 59: 897-911. consistingof a mound of parenchymatoustissue, KIDSTON, R., AND D. T. GWYNNE-VAUGHAN.1912. On in the smallest buds, with two associated cata- the Carboniferous flora of Berwickshire. Part I. phylls. In some cases the bud, which is clothed Stenomyelontuedianum Kidston. Trans. R. Soc. in a mass of multicellularhairs, becomes an axil- Edinb. 48: 263-271. lary branch with abundant secondary tissue. MAHAFFY,J. M. 1975. Morphologyof Microsper- mopterisand occurrencesin Middle Pennsylvanian Oliver and Scott (1904) reportedthe presenceof coal balls. Bot. Soc. Amer.Abstracts. Allen Press, "bud-likestructures" in Lyginop-teris(= Lygino- Lawrence,Kansas. p. 22. dendron) which are borne in the axils of leaves, NAMBOODIRI,K., AND C. B. BECK. 1968a. A com- and are also clothed with long and often glan- parative study of the primary vascular system of dular "emergences." These buds also appear as conifers.I. Genera withhelical phyllotaxis. Amer. young or arrestedbranches in the axils of leaves J.Bot. 55: 447-457. on larger stems. Associated with the axillary , AND . 1968b. A comparativestudy of branch of MicrospermopterisAare groups of the primary vascular system of conifers. II. Genera multicellularepidermal trichomes that also occur with opposite and whorled phyllotaxis. Amer. J. of larger Bot. 55: 458-463. on youngerstems. Additionalspecimens , AND . 1968c. A comparativestudy of stem fragmentsmay yet determinewhether the the primary vascular system of conifers. III. Stelar axillarybranch gave rise to reproductivestruc- evolution in gymnosperms. Amer. J. Bot. 55: tures or was merelyan axillarybud givingrise 464-472. to vegetativefoliage. OLIVER, F. W., AND D. H. SCoTT. 1904. On the structureof the Palaeozoic seed Lagenostoma LITERATURE CITED lomaxiwith a statementof the evidenceupon which it is referredto Lyginodendron.Phil. Trans. R. ANDREWS,H. N. 1942. Contributionsto our knowl- Soc. London. Ser., B. 197: 193-247. edge of AmericanCarboniferous floras: 5. Heter- ROTHWELL, G. W. 1975. The Callistophytaceae(Pteri- angium. Ann. Mo. Bot. Gard. 29: 275-282. dospermopsida): I. Vegetativestructures. Palae- BANKS, H. P., AND M. R. DAVIS. 1969. Crenaticaulis, ontographicaB, 151: 171-196. a new genusof Devonian plantsallied to Zostero- SHADLE,G. L., AND B. M. STIDD. 1975. The frondof phyllum,and its bearing on the classificationof Heterangium. Amer. J. Bot. 62: 67-75. earlyland plants. Amer.J. Bot. 56: 436-449. TAYLOR,T. N., AND R. A. STOCKEY. 1975. The mor- , S. LECLERCQ, AND F. M. HUEBER. 1975. Anat- phologicalnature of Microspermopteris.Bot. Soc. omy and morphologyof Psilophytondawsonii, sp. Amer. Abstracts.Allen Press, Lawrence, Kansas. n. from the Late Lower Devonian of Quebec p. 25-26.