Nord. J. Bot. — Section of structural botany

Wood anatomy of selected and its relationship to habit and systematics

Sherwin Cariquist

Cariquist, S. 1992. Wood anatomy of selectes Cucurbitaceae and its relationship to

habit and systematics. — Nord. J. Bot. 12: 347—355. Copenhagen. ISSN 0l07—055X.

Qualitive and quantitative data are presented on wood anatomy and cambial confor mations of four species of Cucurbitaceae. Although all woody to various degrees, the four species were selected to show a wide range of habits and therefore to discern possible correlations between habit and wood anatomy. Vessels are widely spaced and libriform fibers are minimal where storage of water and carbohydrates is promi nent. Axial parenchyma is dimorphic: lignified thick-walled paratracheal may lend strength to the vessel elements (which are wider than long), whereas thin-walled apotracheal parenchyma may lend flexibility to stems (especially in lianoid species) and serve for storage. Rays are multiseriate only and alter little from primary rays (but large multiseriate rays originate suddently in fascicular areas of one species). Distribution and abundance of libriform fibers relate to habit: most abundant in the shrubby Acanthosicyos, least in the storage-oriented lower stems of Apondanthera). Vasicentric tracheids extend radially and interconnect vessels, potentially providing a subsidiary conductive system that would maintain the conductive pathways of the large vessels if some of those vessels were to be disabled or deactivated. ceae are characterized by septate fibers, vasicentric tracheids, and storied wood structure. Each of these features is found in at least half of the families now commonly included in Violales, to which Cucurbitaceae are thought to belong.

S. Cariquist, Rancho Santa Ana Botanic Garden and Dept of Biology, Pomona College, Claremont, California 91711, USA.

Introduction Coccinia grandis J. A. Voigt is a rain forest liana al though with moderate woodiness (up to about 10 cm in Cucurbitaceae are a family often thought to be non- diameter); the stems at my disposal are 5 cm in diame woody. Indeed, Metcalfe & Chalk (1950), who for most ter. Zanonia indica L. is a rain forest vine in which only families of dicotyledons devote a section to “wood” a limited amount of secondary growth occurs in the omit such a section for Cucurbitaceae. There are, how vascular bundles. The features of vessels, imperforate ever, several Cucurbitaceae that become moderately tracheary elements, axial parenchyma, ray parenchyma, woody. Four of these have been selected because they and variant cambial types are analyzed with respect to represent divergent habits that may form the basis for habit of these four species. Although Zimmermann’s correlations between habit and wood anatomy. Acan (1922) neglected but magnificent monograph on Cucur thosicyos horridus Weiw, is a shrub of Namibian sand bitaceae contains much anatomical information, the dunes; the lower stem, usually buried beneath the sand, wood histology of the family has needed characteriza may develop a woody cylinder 1—2 cm in diameter. tion and analysis. Apodanthera undulata A. Gray, from arid areas of New Wood anatomy of Cucurbitaceae is of interest with Mexico, has a tuber-like storage root; the base of the respect to systematics. Older systems placed Cucurbita stern forms a woody transition to this storage organ. ceae in an order such as Campanulales, along a line

Accepted 28—11—1991 © NORDIC JOURNAL OF BOTANY NORD J. BOT 12: 347—355

Nord. J. Bot. 12 (3) (1992) 347

parenchyma.

axial

apotracheal tap

thin-walled

xylem: sx secondary phloem secondary = sp axial parenchyma; = = paratracheal sclerified

sap

fibers, libriform If

= cambium,

cam Symbols: sm).

10 = (divisions 2 Fig. scale above shown = 2—4. Figs sm); — 10

=

divisions I Fig. (finest above shown scale 1, Fig. evident. parenchyma axial the of thin-walled storied nature one of — left; portion

right,

at ray multiseriate

large cylinder; woody main from wood of section Tangential 4. Fig. parenchyma. axial thin-walled — of

distributon and cells, ray sclerified below), and the above ray, cells (traversing ray perforated cylinder, show to main woody from

xylem secondary of 3. Transection Fig. cambium. by this formed xylem in secondary are the fibers as libriform as — well vessels

strand; phloem

intraxylary to abaxial cambium by strand formed Vascular 2. Fig. areas. fascicular two the in abruptly — begin

rays multiseriate top, at pith; the in strands phloem to abaxial by intraxylary cambium a produced fibers) libriform few a (plus

phloem secondary of zones two showing Transection, 1. Fig. 8086).— (Carlquist horridus Acanthosicyos of sections

Stem 1—4. Figs

•1 L..iii’ 4

SAt

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il’c

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A tap

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. , a--- L_ Figs 5—8. Wood sections of Cucurbitaceae. — Fig. 5. Acanthosicyos horridus (Carlquist 8086). transection of cambial region to show contrast between cambium in ray area and fascicular in region; sciereids in ray, below. — Fig. 6. Apodanthera undulata (Fosberg 53738), portion of vessel wall from tangential section, to show wide grooves interconnecting pits apertures. — Figs 7—8. Coccinia grandis (J. B. Fisher 88—23). — Fig. 7. Wood transection; ray cambia have produced two pockets of secondary phloem along the fascicular area in which several vessels and associated libriform fibers are present. — Fig. 8. Tangential section; ray in center; storying evident in axial parenchyma. — Figs 5, 7, 8, scale above Fig. 2; Fig. 6, scale above Fig. 6 (divisions = 10 sm). — Symbols: cam = cambium in fascicular area; If libriform fibers; rc = cambium in ray area; sap = sclerified paretracheal axial parenchyma; sp = secondary phloem; tap = thin-walled axial parenchyma.

Fig. 1. 12, above 10, scale Fig. 2; Fig.

scale above 11, 9, Figs stem. of tangential section pits, bordered from large tracheids, showing vasicentric of Portions 12. — Fig.

stem. of

from transection vessels) (large xylem secondary strand 11. 10037). with Vascular Fig. — (Hartley indica — ll—12.Zanonia

Figs. fibers. libriform left, at two and, of wall, left the vessel the to parenchyma — axial (right), wall showing vessel wood,

of section of tangential Portion 10. Fig. it. of left and right the to rays area of fascicular with a vessels stem, showing lower — from

wood of 9. Transection 53738). Fig. (Fosberg undulata Apodanthera

9—10. Figs Cucurbitaceae. of Wood

sections 9—12. — Fig. —

-— ii[

;.-% j-: ;:‘

‘fr __ leading to Asterales (e.g., Wettstein 1935). In more calculations do not readily reveal the nature of the recent systems, however, Cucurbitaceae is uniformly wood. Obviously, vessel density drops markedly in the placed in Violales (Cronquist 1981, 1988; Dahlgren highly parenchymatous stems and roots in which storage 1975, 1980; Takhtajan 1980; Thorne 1976, 1983). Be of carbohydrates and water is prominent. cause wood histology of Cucurbitaceae has not hitherto been summarized or analyzed, the ways in which wood features of the family may relate to systematics have not been hitherto presented. Anatomical descriptions Acanthosicyos horridus Secondary xylem produced by growth that increases the Materials and methods radial extent of the bundles of the primary stem as well as by cambial action adjacent to the strands of intraxyl Wood of Cucurbitaceae offers problems for sectioning ary phloem. Growth rings absent, although mild fluc in two respects: it is softer than most woods sectioned utation in diameter of vessels evident (Fig. 3). Vessels successfully on a sliding microtome, and the large ves mostly solitary (Figs 1, 3); mean number of vessels per sels are likely to fracture during sectioning on a sliding group, 1.32. Mean diameter of vessels, 128 Ism. Mean microtome. However, the wood of Cucurbitaceae is vessel element length, 89 sm. Mean vessel wall thick hard enough so that it cannot be sectioned successfully ness, 5.2 lAm. Perforation plates simple. Lateral wall by the ordinary paraffin methods that involve sectioning pitting of vessels alternate; pits 6—9 im in diameter. Pit with a rotary microtome. An ideal method that solves apertures elliptical or wider; when wider, forming these problems involves softening of the wood with grooves that interconnect pit apertures. Narrow vessels ethylene diamine, followed by embedding in paraffin and vasicentric tracheids, often with distorted shapes and sectioning on a rotary microtome (Carlquist 1982). that are variously rectangular in longitudinal section A very important element in this method is the soaking present, interconnecting vessels or vessel groups radi in water of exposed surfaces of paraffin-embedded ma ally. All other imperforate tracheary elements are sep terial prior to sectioning; sectioning of tissues that have tate libriform fibers with simple pit s. Mean libriform not been subjected to the soaking process is much less fiber length, 539 p.m. Mean libriform fiber diameter at effective. widest point, 32 p.m. Mean libriform fiber wall thick Sections were stained with safranin and fast green. ness, 5.2 p.m. Axial parenchyma of two types: para Macerations were prepared by means of Jeffrey’s fluid tracheal thick-walled lignified cells (“sap” in Fig. 4) and and stained with safranin. thin-walled nonlignified cells that are clearly storied in The material of Acanthosicyos horridus was collected tangential sections (“tap” in Fig. 3, 4). Paratracheal in Namibia in 1989, thanks to a grant from the Amer parenchyma cells distorted in shape by vessel enlarge ican Philosophical Society. Jack Fisher of the Fairchild ment; pits of paratracheal parenchyma cells bordered Tropical Garden kindly provided the material of Cocci (bordered pit pairs) facing vessels, but pits simple on nia grandis. Material of both of these species was fixed other walls. Thin walled axial parenchyma cells present in formalin acetic alcohol. Material of the two other as variously shaped bands or patches as seen in transec species was dried, and was obtained from specimens in tion (Figs 3, 5), but fusiform or, less commonly, in the herbarium of the Rancho Santa Ana Botanic Gar strands or two cells as seen in longitudinal section (Fig. den; this material was soaked in water prior to the 4). Rays all multiseriate, averaging more than 10 cells microtechnique methods mentioned above. wide at their widest point (Fig. 4, left and right). A few The terms used are according to the IAWA Commit multiseriate rays originate not by widening of narrow tee on Nomenclature (1964). The term “vasicentric tra rays, but suddenly (Fig. 1, upper left and upper right). cheid” and terms for cambial variants are as in Carlquist Ray cells predominantly upright; very few square or (1988); I believe that these usages reflect the intent of procumbent cells present. Ray cells thin walled or scle the AIWA Committee on Nomenclature (1964), but reids; the sciereids isolated or in groups (Fig. 4, upper because few wood anatomists at that time were familiar left, lower right; Fig. 5). Sclerotic ray cells with bor with these phenomena, the definitions given there for dered pits. Storying evident in axial parenchyma and these terms were vague and incomplete. Vessel diame some vessels. Tyloses present in many vessels (Fig. 2, ter in the descriptions is computed as lumen diameter at upper left; Fig. 3, upper center). widest point. Very narrow vessels that are similar to The strands of intraxylary phloem in Acanthosicyos vasicentric tracheids and cannot be readily identified in horridus develop at their adaxial faces cambia that pro transections are not included in the figures on vessel duce secondary phloem abaxially and secondary xylem diameter. Number of vessels per mm2 is not computed adaxially—an orientation contrary to that produced from for Cucurbitaceae because the amount of ray tissue and a “normal” cambium (Figs 1, 2). The strands produced axial parenchyma differs so much from one species to by the cambium adjacent to intraxylary phloem in Fig. 1 another or one part of the to another, so that contain mostly secondary phloem, with secondary xy

Nerd. J. Bet. 12 (3) (t992) 351 tern only as a few libriform fibers. The strand shown in cells. In fact, fewer cells than appear present occur Fig. 2 is characterized by addition of a few vessels as here. The vertical walls of the parenchyma cells imme well as libriform fibers. Phloem fibers demarcate the diately outside of the vessel are much lobed; a longitudi innermost margin of the phloem in these strands (Figs 1, nal section of these interfingering lobes results in the 2), and crushed phloem cells can be found in the older appearance shown. The lobed nature of axial paren phloem tissue of the strands. There are perforated ray chyma cells facing vessels was illustrated for Cucurbita cells in Acanthosicyos horridus, evident by a series of ceae by Zimmermann (1922) for wood of Peponium. vessel elements derived from ray initials traversing ray areas (Fig. 3, center above and center below). The cambium of the main vascular cylinder shows marked Coccinia grandis differences between the axial and ray areas (Fig. 5). The ray cambium (“rc”) consists of slow-paced divisions: Secondary xylem in plates representing extensions of few but large cells are added to secondary xylem rays the primary stem. Vessels mostly solitary (Fig. 7); mean and secondary phloem rays in contrast to the numerous number of vessels per group, 1.13. Mean vessel diame narrow cells added by the actively dividing cambium of ter, 195 tm. Mean vessel element length, 73 tm. Mean the axial zones (“cam”). vessel wall thickness, 3.8 m. Perforation polates sim ple. Pits of lateral vessel walls alternate, circular, 5—8 t.tm in diameter, apertures slitlike, some interconnected by grooves. Apondanthera undulata Imperforate tracheary elements consisting of libriform fibers in the vicinity of vessels (“If” in Figs Wood of lower stem described unless otherwise noted. 7, 8). Libriform fibers septate, pits simple. Libriform Wood consisting of plates of vessels (Fig. 9), vessels and fibers forming an aliform or paratracheal arrangement their associated lignified paratracheal parenchyma sepa with relation to vessels as seen in transverse section, reted from each other by thin-walled parenchyma in the often forming a pair of lateral bands flanking a vessel. upper root. Vessels solitary (Fig. 9). Mean vessel diam Vasicentric tracheids often rectangular in longitudinal eter, 141 tm. Mean vessel element length, 75 ttm. Mean section, but variously shape, forming radial intercon vessel wall thickness, 5.4 tm. Perforation plates simple. nections between vessels. Axial parenchyma of two Lateral wall pitting of vessels consisting of basically sorts: lignified thick-walled paratracheal, and nonligni alternate circular pits. The shape and arrangement of fied thin-walled apotracheal. The paratracheal paren the pits is altered somewhat by the presence of wide pit chyma (Figs 7, 8) forms sheaths two to four cells thick apertures which are interconnected by grooves, or coa around the vessels. The cells adjacent to the vessels lescent pit apertures (Fig. 6). Wall portions between the have undulate walls as seen in longisection (Fig. 8, horizontal rows of pits are notably thick (Fig. 6; thick “sap”). Apotracheal parenchyma in the form of bands enings seen in sectional view, Fig. 10). Vasicentric tra or variously shaped patches between vessels (and their cheids are absent. All imperforate tracheary elements associated libriform fibers) as seen in transection, sto are septate libriform fibers with simple pits (Fig. 10, ried as seen in longisection (Fig. 8, “tap”). Apotracheal left). Libriform fibers in small numbers are adjacent to parenchyma cells mostly not subdivided, but some cells some vessels in the lower stem, but are absent from in strands of two cells. Rays all multiseriate, averaging roots. Axial parenchyma of two sorts: lignified thich more than 10 cells wide at their widest points. Ray cells walled paratracheal, and nonlignified thin-walled apo predominantly upright, few square or procumbent cells tracheal. The paratracheal parenchyma forms sheaths present. Ray cells all thin walled (Figs 7, 8). Para two to four cells thick around the vessels (Fig. 9). The tracheal axial parenchyma and some vessels conforming thin-walled apotracheal parenchyma forms the ground to the storied pattern. Tyloses present in some vessels; tissue of the secondary xylem (other than vessels, para starch seen in some tyloses. tracheal parenchyma, and the very few libriform fibers) Ray cambia (term from Carlquist & Hanson, (1991)) and is much more abundant in the root than in the stem form along the margins of rays and add, at first, second base. Apotracheal parenchyma is storied. Rays are all ary phloem (“sp, “ Fig. 7). My material did not show multiseriate, averaging more than 10 cells wide at their secondary xylem formed by the ray cambia, but Zim widest point. The multiseriate rays are essentially exten mermann (1992) does figure secondary xylem as well as sions of primary rays. Ray cells are predominantly up secondary phloem formed by ray cambia in Coccinia right, square or procumbent cells few. All ray cells are engleri; secondary phloem on the distal (ray) side of the thin walled and nonlignified. Tyloses in some vessels. cambia, secondary xylem on the proximal side. The gray patches to the left and right of the vessels, lower left, in Fig. 9 are areas of phloem crushed as a result of addition of secondary phloem by ray cambia in Zanonia indica much the same fashion as described for Coccinia grandis below. The lignified parenchyma just to the left of the Secondary xylem representing extensions of the primary vessel, Fig. 10, appears subdivided into a series of oval bundles (in Fig. 11, probably the five largest vessels and

352 Nord. J. Bot. 12 (3) (1992) associated imperforate tracheary elements are second as a feature that may, by virtue of the flexibility pa ary xylem, the zone with the smaller vessels is primary renchyma confers, protect large and therefore vulner xylem). Secondary xylem vessels mostly solitary; mean able vessels against torsion (Cariquist 1985b, 1991; Putz number of vessels per group, 1.10. Mean vessel diame & Holbrook 1991). The stems of Zanonia (Fig. 11) are ter, 141 im. Mean vessel element length, 92 tm. Mean understandable in this regard: the strands of secondary vessel wall thickness, 5.0 im. Imperforate tracheary xylen are arranged in background of soft parenchyma, elements consisting of libriform fibers with simple pits and the vessels are sheathed in thick walled libriform and fusiform vasicentric tracheids (Fig. 12); in my mate fibers and vascientric tracheids. rial, the vasicentric tracheids are more abundant than The dimorphism of axial parenchyma in woods of the libriform fibers. Axial parenchyma of two sorts: Cucurbitaceae studied here, as well as those described paratracheal cells with thick lignified walls, and apotra by Zimmermann (1922), may be correlated to the scan- cheal cells with thin nonlignified walls. Paratracheal dent habit. The lignified thick walls of the paratracheal parenchyma forming a sheath one to three cells thick parenchyma may prevent damage to vessels by enhanc around vessels. Axial parenchyma present only as ing their mechanical strength while the patches of thin- strands near the periphery of the vascular strands; the walled apotracheal parenchyma may offer enhanced apotracheal parenchyma is evident as indentations in flexibility to the stem and may thereby protect vessels the outline of the vascular strand shown in Fig. 11. when torsion occurs. The wide, tall rays composed of Paratracheal parenchyma either not subdivided or in thin-walled parenchyma in Cucurbitaceae, like those in strands of two cells. Little secondary growth present in woods of other scandent plant, may be of greater signif ray areas, which are little more than the primary rays, icance than axial parenchyma by offering a tissue that compressed somewhat by the expansion of the vascular can yield to twisting and protect the plates of axial bundles by their secondary xylem additions (Fig. 11). xylem (which include vessels) against fracture. Perhaps quite significant in this regard is that the only new rays initiated in Cucurbitaceae are wide and tall (Fig. 1), an unusual mode of ray origin because in most dicotyle Conclusions about wood histology and its dons, rays originate as narrow (often uniseriate) and relation to habit gradually widen ontogenetically. Exactly the same phe nomenon of sudden origin of wide, tall rays from the The various features of the wood of Cucurbitaceae can cambium occurs in another family with a similar range almost all be related, directly or indirectly, to the scan- of habits, Aristolochiaceae (Carlquist, unpubi.). These dent habit characteristic of the vast majority of the examples, in turn, remind one of the overrepresentation species. The wood feature most often cited as character of succesive cambia and other cambial variants that istic of scandent is wide vessel diameter, which provide abundance of parenchyma in lianoid dicotyle tends to compensate for the small transectional area of dons (for listing, see Carlquist 1991). The distribution of secondary xulem (considering the amount of foliage libriform fibers in Coccinia grandis (Fig. 7) suggests supplied) In climbing plants (see literature cited in Carl enhanced strength and protection of the integrity of quist 1985b). Cucurbitaceae are notable for wide mean vessels without loss of flexibility in stems. lumen diameter (average of the four species, 164 im). The presence of vasicentric tracheids was reported Note should be taken that narrow vessels, comparable earlier in Zanonia (Carlquist 1985); they are abundant in diameter to vasicentric tracheids, were not included in secondary xylem of this species. Vasicentric tracheids in vessel diameter measurements in Acanthosicyos hor are less abundant in Acanthosicyos horridus and Cocci ridus or Coccinia grandis because in transection narrow nia grandis, and are similar enough in transection to vessels cannot readily be distinguished from libriform narrow vessels and libriform fibers so that the vasicen fibers. The vessel elements in the Cucurbitaceae sur tric tracheids could not be illustrated photographically veyed here are notable for having greater average diam so as to distinguish them from these other cell types. eter than length (average length for the four species, 82 The distribution of vasicentric tracheids in Acanthos Im, exactly half the average vessel diameter of the four icyos horridus and Coccinia grandis is much like that species). The shortness of vessel elements is primarily figured by Zimmermann (1922) for the secondary xylem an expression of the high degree of specialization of of Peponium: radial plates of vasicentric tracheids wind wood features in Cucurbitaceae. The wall thickness of through the radial bands of secondary xylem, intercon vessels in the species studied (mean = 4.9 ftm) is ap necting vessels. Note should be taken that narrow ves proximately twice the thickness typical in dicotyledons sels may be intermixed with these vasicentric trachieds, as a whole. Thick vessel walls seem related to the great but probably have much the same physiological signif diameter of the vessels. The band-like thickenings on icance. The interconnection of vessels by means of vas vessel walls (Fig. 10) may be another indication of en icentric tracheids in lianoid woods was cited earlier as a hanced wall strength that compensates the great diame structural mode potentially offering conductive safety in ter of the vessels in woods of vines. The abundance of that conductive pathways could be maintained even if parenchyma in wood of scandent plants has been cited particular vessels were embolized (Carlquist 1985,

Nord. J. Bot. 12 (3) (1992) 353 1987). One species in the present study, Apodanthera bitaceae. A third type of cambial variant not present in undulata, lacks vasicentric tracheids. In this species, Cucurbitaceae studied here, but reported by Zimmer vessels are more widely spaced than in the other spe mann (1922) for the Mormodica is the occurrence cies, and are spaced apart from each other in many of occurrence of successive cambia. These three cambial instances by thin-walled parenchyma. Vasicentric tra variants may have similar topographic and physiological cheids might not be expected to traverse this thin-walled significance: providing strands of vascular tissue that do parenchyma. In addition, Apodanthera has abundant not increase the thickness of a single woody cylinder parenchyma devoted to storage of water and starch, and but, instead, form vascular strands separate from the in a succulent organ, safeguarding of conductive path main cylinder. The net effect appears to be provision of ways may have a lower selective value than in secondary a greater flexibility by means of dispersion of vascular xylem of stems and roots of nonsucculent species. Zim strands in a background of soft parenchyma likely to mermann (1922) uses the term “Quertracheid” (litera protect the integrity of vascular tissues during torsion lly, “transverse tracheid”) to denote what I term vas (Carlquist 1985b, 1991; Putz & Holbrook 1991). icentric tracheids. Perhaps the “transverse” in his term alludes to the horizontal interconnections among vessel provided by these vasicentric tracheids. The identity of the “Quertracheiden” mentioned by Zimmermann does not seem to have been mentioned or appreciated in any Systematic conclusions subsequent literature. If Cucurbitaceae belong to Violales, as modern phylo The above paragraphs detail possible correlations be genetic systems claim, the family is different from most tween scandent habit and features of wood anatomy. others in the order in its vining and lianoid habit. Pas However, the reader will note what two of the species sifloraceae are the only other violaLean family in which studied (Acanthosicyos horridus and Apodanthera un these habits are common. Obviously, wood features dulata) are not really scandent. I believe that these that represent modifications of the wood plan to suit the species are phyletically close to scandent species and scandent habit cannot be used to construe relationships have been derived from them: the vast majority of of Cucurbitaceae. Wood features of Cucurbitaceae wor Cucurbitaceae are scandent, and the genera apparently thy of consideration as indicators of relationship are: ancestral, judging from their placement in phyletic sys septate libriform fibers; vasicentric tracheids; and story tems, in each subfamily are scandent. In this case, one ing of wood. In the following listings, only families may assume that time has been insufficient for the xyl commonly assigned to Violales according to the phylo ary conformations of a scandent phylad to have genetic systems cited in the Introduction are mentioned. changed, or else that these xylary features are not of Septate libriform fibers are found in Begoniaceae, Fla negative selective value in the growth forms of Acan courtiaceae, Lacistemaceae, Passifloraceae, and Vio thosicyos and Apodanthera. Laceae (Carlquist 1988); all families of Violales possess The fact that no uniseriate rays are formed in the libriform fibers, but septate fibers have not been re vascular cambium of Cucurbitaceae, and only a few ported in the families other than those just listed. Vas large multiseriate rays are ever initiated during second icentric tracheids are found in Ancistrocladaceae, Fla ary growth may have a significance in providing flexibil courtiaceae, Frankeniaceae, Malesherbiaceae, Passiflo ity as stated above. Lack of uniseriate rays may also be, raceae, Turneraceae, and a few Violaceae. Storied in Cucurbitaceae, a phenomenon allied to raylessness wood structure occurs in Begoniaceae, Cochiosperma and the tendency of raylessness to occur in woods of ceae, Datiscaceae, Frankeniaceae, Tamaricaceae, and a herbaceous dicotyledons or (in all likelihood) of second few Violaceae. Obviously none of the three wood fea arily woody dicotyledons derived from herbaceous an tures unites all families commonly placed in Violales cestor (Carlquist 1988). A similar condition occurs in (Achariaceae and Caricaceae can be placed out of con Aristolochiaceae (Carlquist, unpubl.), perhaps for the sideration because of the herbaceousness of Acharia same reasons. The range of growth forms in Aristo ceae and the highly parenchymatous nature of second lochiaceae is similar to that in Cucurbitaceae, and both ary xylem in Caricaceae). At least half of the families of families can be suspected of being basically herbaceous, Violales possess the three features cited, however. This however woody other families in their respective orders distribution provides sufficient resemblance among the may be. families so that each of these features should be consid Zimmermann (1992) reports ray cambia, also found ered as potential indications of relationship. None of in Convolvulaceae (Carlquist & Hanson 1991) in Cocci the three features cited characterizes the majority of nia engleri. In the present study, Cocconia grandis also families of dicotyledons; widespread features (e. g., has ray cambia (Fig. 7). A second cambial variant os simple perforation plates) are not good indicators of represented by cambial formation abaxial to the strands relationship. of intraxylary phloem; this variant is represented here by Acanthosicyos horridus (Figs 1, 2). Zimmermann (1922) reports this variant for sevaral genera of Cucur

354 Nord. J. Bot. 12 (3) (1992) Dahigren, R. M. T. 1975. A system of classification of the References angiosperms to be used to demonstrate the distribution of

characters. — Cariquist, S. 1982. The use of ethylenediamine in softening Bot. Notiser. 128: 119—147. — . 1980. A revised system of classification of the angios hard plant tissues for paraffin sectioning. — Stain Techn. 57: 311—317. perms. — Bot. journ. Linnean Soc. 80: 91—124.

— IAWA Committee on Nomenclature. 1964. . 1985a. Vasicentric tracheids as a drought survival mecha Multilingual glos nism in the woody flora of southern California and similar sary of terms used in wood anatomy. — Konkordia, Winter thur, Switzerland. regions; rewiew of vasicentric tracheids. — Aliso 11: 37—68.

— Metcalfe, C. R. & Chalk, L. 1950. Anatomy of the dicotyle . 1985b. Observations on the functional wood histology of vines and lianas; vessel dimorphism, tracheids, vasicentric dons. — Clarendon Press, Oxford. POtz, F. E. & Holbrook, N. M. 1991. Biomechanical studies of tracheids, narrow vessels, and parenchyma. — Aliso 11: 138—157. vines. — In: Putz, E E. & Mooney, H. A. (eds), Biology of vines. Cambridge University Press, Cambridge, 13—97. — pp. 1988. Comparative wood anatomy. — Springer Verlag, Berlin & Heidelberg. Takhtajan, A. L. 1980. Outline of the classification of flower

— ing plants (Magnoliophyta). — Bot. Rev. 46: 225—359. . 1991. Anatomy of vines and liana stems: a rewiew and Thorne, R. F. 1976. A phylogenetic classification of the An synthesis. — In: Putz, F. E. & Mooney, H. A. (eds), Biology giospermae. — Evol. Biol. 9: of vines. Cambridge University Press, Cambridge, pp. 35—106. — . 1983, 53—71: Proposed new realignments in the angiosperms. — Nord. J. Bot. 3: 85—117. — & Hanson, M. A. 1991. Wood and stem anatomy of Wettstein, R. 1935. Handbuch der systematischen Botanik. Convolvulaceae: a survey. — Aliso 13: 51—94.

Vierte — Cronquist, A. 1981. An integrated system of classification of AufI. Franz Deuticke, Leipzig & Wien. Zimmermann, A. 1922. Die Cucurbitaceen. Beiträge flowering plants. — Columbia University Press, New York. zur Anatomie, Physiologie, Morphologic, Biologic, — 1988. The evolution and classification of flowering plants. Patholo gic, und Systematik. — Gustav Fisher, Jena. ed. 2. — The New York Botanical Garden, Bronx, New York.

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