Wood and Bark Anatomy of Gneturn Gnemon L

Botanical Journal oft/ic Linnean Society (1994), 116: 203—221. With 34 figures

Wood and bark anatomy of Gneturn gnemon L.

SHERWIN CARLQUIST F.L.S.’

Santa Barbara Botanic Garden, 1212 Mission Canjon Road Santa Barbara, CA 93105, US.A.

Received March 1994, acceptedfrr publication August 1994

Quantitative and qualitative data are presented for seven collections representing two varieties (unlike in habit) of Gneturn gnemon. Tracheids are present, but abundant and iniermixed with them are septate fibre-tracheids rich in starch. Axial parenchyma has been reported only once previously for the species. Axial parenchyma is in strands of 4—10 cells, is rich in starch, is primarily vasicentric (paratracheal) in distribution, less commonly diffuse. About equally common are simple and compound perforation plates; the latter are composed of from two to about ten bordered foraminate perforations, the shape of which may be altered by crowding or coalescence, but is clearly still foraminate. Lateral walls of vessels hear pits that are vestured around pit cavities, not facing the pit membrane. Rays are composed mostly of procumbent cells; the tangential walls bear bordered pits. Crystals, present in ray cells and (rarely) axial parenchyma vary widely in size. Crystalliferous sclereids with layered walls, starch-rich parenchyma, and gelatinous secondary phloem fibres are the main components of bark. Early stages in origin of successive vascular cambia in bark are newly described. When representative conditions are derived from study of large numbers of slides, the classical view that Gnetum vessels are unlike those of angiosperms is supported. Features of Gneturn gnemon wood are discussed in the lighi of ecology and conductive physiology.

ADDITIONAL KEY WORDS:—angiosperm — evolution -- ecological wood anatomy Onetales -

gymnosperms — successive cambia — variant wood structure.

CONTENTS

Introduction 203 Material and methods 205 Anatomical results 206 Vessel elements 206 Imperforate tracheary elements and axial parenchynsa 213 Rays 213 Crystals 215 Growth rings 215 Bark anatomy and variantcambial activity 217 Conclusions 217 References 220

INTRODUCTION Data on wood anatomy of Gnetales have been available from scattered observations on a few species. Our knowledge was inaccurate and incomplete in numerous respects. Attempts to improve our knowledge with comparative

TABLE 1. Vessel features of Gnetum gnemon.

1 2 3 4 5 6 7 Variety Collection VG VD VM VL VWT PP LP gneinon Carlquist 1329 1.09 70 12.7 1082 2.5 2.0 11.5 gnemon Cariquist 8088BF 1.03 94 12.1 1389 4.4 3.5 12.0 gnemon Cariquist 8088YS 1.24 85 22.9 1193 4.3 3.1 10.4 gnemon Cariquist 8088R 1.10 78 23.5 1254 4.0 1.3 11.5 gnemon PRFw-19814 1.02 129 8.8 1574 2.5 1.0 11.5 gnemon SJRw-25309 1.15 82 25.7 1127 5.0 1.7 10.0 tenensm Aw-12395 1.03 39 47.4 1029 2.0 2.0 9.2 Collections averaged 1.09 82 21.1 1235 3.5 2.0 10.9

Key: I VG, mean number of vessels per group; 2 VD, mean vessel diameter, pm; 3 VM, mean number of vessels per mm2; 4 VL, mean vessel element length, pm; 5 VWT, mean vessel wall thickness, pm; 6 PP mean number of perforations per perforation plate; 7 LP, mean diameter of lateral wall pits. Collections are all mature stem portions except for Carlquist 8088, in which BF = basal stem flange, R = root, and YS = young stem. study of the wood and bark anatomy of Ephedra have recently been made (Cariquist 1989, 1992). For Gnetum, limited data based on only a few species have been published, chiefly in terms of the summaries found in Maheshwari & Vasil (1961) and Martens (1971). The data in these compilations do not include quantitative features, do not indicate the presence of imperforate tracheary elements other than tracheids, and do not describe axial parenchyma. The latter two features were noted for G. gnemon by Greguss (1955), who did not describe any other species of the genus, and whose description of G. gnemon wood is not entirely accurate. Existing references state that growth rings are absent in Gnetum (they are infrequently present), and that tori are absent in pits of tracheary elements (they are clearly present in some species of Gnetum). IViuhammad & Sattler (1982) have figured selected vessels of Gnetum in an attempt to show that Gnetum vessels are more like those of angiosperms than has hitherto been believed, but their sampling definitely does not show what one finds when more material is examined. To be sure, the account of Muhammad & Sattler (1982) worked with primary xylem. The present account is based on secondary xylem, although primary xylem is present in some of the wood sections and has been observed also. Wood anatomy of Gnetum has likely been neglected by wood anatomists because wood of most species is not readily available. In addition, ordinary microtechnical procedures (e.g. sectioning on a sliding microtome) do not work very well in the genus. The products of successive cambia in the lianoid species present difficulties, and even in G. gnelnon, wood cells tend to shred even when cut with the sharpest of knives. Alternative methods have therefore been employed in the present paper. A series of papers, of which this is the first, is contemplated in order to offer a better knowledge of the wood anatomy of Gnetum. That of G. gnemon is so different from the other species that a separate paper is warranted. Gnetum gnemon ranges from shrubby to truly arboreal, and those extremes are represented in the specimens studied here. The former habit characterizes G. gnemon var. tenerum Markgraf. The arboreal habit is represented in the remaining specimens (Tables 1, 2), all of which are referable to G. gnemon var. gnemon (some of these specimens were formerly termed G. gnemon var. domesticum (Rumphius) Markgraf, GJ\IETUM GJsIEMOJf WOOD AND BARK 205

TABLE 2. Imperforate tracheary element and parenchyma features of Gnetum gnemon.

Variety Collection 1 2 3 4 5 6 7 8

ITL lTD TWT TPD FTP MRH URH MW gnemon Cariquist 1239 1608 75 4.3 13.8 4.6 1069 146 5.6 gnelnon Cariquist 8088BF 1766 34 6.0 10.4 4.4 1392 207 3.4 gnemon Carlquist 8088YS 1824 34 5.2 10.4 4.0 1390 207 3.3 gnemon Carlquist 8088R 1764 37 5.2 10.3 4.6 1148 203 3.6 gnemon PRFw-19814 1907 37 6.0 11.5 4.5 1657 282 6.7 gnemon SJRw-15398 1484 35 5.0 9.9 6.9 2302 206 4.5 tenerum Aw-l2395 1483 23 2.0 6.9 4.6 1355 214 3.7 Collections Averaged 1691 32 4.8 10.5 4.8 1616 209 4.4

Key: 1 ITL, mean length of imperforate tracheary elements, pm; 2 lTD mean diameter of imperforate tracheary elements, pm; 3 TWT, mean wall thickness of tracheids, pm; 4 TPD, mean diameter of tracheidpits, pm; 5 FTP, mean diameter of fibre-tracheid pit cavities, pm; 6 MRH, mean height of multiseriate rays, pm; 7 URH, mean height of uniseriate rays, pm; 8 MW, mean width of multiscriate rays, cells. Collections

are all mature stem portions except for Carlquist 8088, in which BF = basal stem flange, R = root, and YS = young stem.

as noted by Markgraf (1930, 1951). Wood of various portions of a tree of G. gnemon var. gnemon have been studied here, and appreciable organographic differences are evident. The only Gnetum species close to G. gnemon is G. costatum K. Schum. Wood of G. costatum was not available for study, but because these two species differ oniy in minor features, their woods are likely similar. The significance of wood anatomical findings in Ephedra, Gnetum and Wdwitschia will be assessed in the final paper of this series. The relationships of Gnetales have been a subject of great interest and controversy for many years. New information from any data set is likely to be helpful in improving our understanding of the phylogenetic origins of Gnetales, origins just as obscure as those of angiosperms but less discussed only because angiosperms are so much more conspicuous.

MATERIAL AND METHODS Tables I and 2 give quantitative features for the five collections studied. Three portions of the collection Cariquist 8088 have been studied. This specimen, a tree on the campus of the University of Malaysia, Kuala Lumpur, readily provided material of roots because roots at the ground surface could be readily cut. Also, this tree was old enough to begin forming buttresses at the base, and wood and bark from a young buttress were used. Seedlings of G. gnemon of various sizes could be found in untended areas of forest nearby on this campus, and one of these provided material of the young stems. Wood and bark from the portions of Carlquist 8088 were preserved in 5O°/o aqueous ethyl alcohol. Materials of the remaining collections were available as dried specimens. The provenance of these specimens is as follows (xylarium abbreviations from Stern, 1988): G. gnemon var. gnemon, Carlquist 1329 (RSA), lowland rain forest near Lae on the road to Wau, New Guinea; G. gnemorz var. gnemon, PRFw 19814, Solomon Islands; G. gnemon var. gnemon, SJRw-25398, 6 miles from Suva on main road; G. gnetnon var. teneruin, Aw-32395 (voucher specimen, Abbe 9899), shrub l2 m high, primary forest on ridge, south-east of Tolok Delima, Bako National Park, Sarawak, Malaysia. For one collection (Figs 1, 2), a slide was 206 S. CARLQUIST available from the Harvard Wood Collection (Aw), but no wood specimen was available. Although some sliding microtome sections were prepared, the most satisfactory preparations were obtained by softening the woods in ethylene diamine, followed by embedding in paraffin and sectioning on a rotary microtome Carlquist, 1982). Woods of Gnetum are harder than those typically sectioned with this method, so that longer exposure to ethylene diamine was required. Sliding microtome sections, dried between clean glass slides, were used for the SEM photographs. Material to be studied with SEM was not treated with sodium chlorite, a method that removes incrustations, because I wished to induce a minimum of changes in wall details. Portions of each wood collection were treated with Jeffrey’s Fluid and stained with safranin to obtain macerations. Wood terminology follows that of the IAWA Committee on Nomenclature (1964), but on account of the distinctive features of Gnetum gnemon, refinements are required. One worker, Greguss (1955) has correctly differentiated tracheids from fibre-tracheids in G. gnernon; a similar definition was employed for Ephecira (Carlquist, 1989). Vessel diameter is measured as the widest diameter of the lumen. Quantitative data are derived from 25 measurements per feature except for pit diameter and wall thickness, in which typical conditions are measured. The assistance of David C. Michener in helping me obtain material from the Harvard Wood Collection (Aw is acknowledged. Dr Regis Miller put material from the Forest Products Laboratory collections at my disposal.

ANATOMICAL RESULTS Vessel elements Table 1 shows quantitative vessel features for the collections studied. Vessel grouping (Table 1, column 1) is low in Gnetum (Figs 1, 3, 5, 7, 8). Occasionally a pair of vessels may he seen (Fig. 1, upper left), but rarity of pairs is indicated by the average number of vessels per group in the species as a whole, 1.09. Such a low figure is probably close to what one would expect if vessels with diameters like those of G. gnemon were placed randomly. The diameter of 0. gnemon vessels (Table 1, column 2) is rather wide compared with vessel diameter of xeric angiosperms, hut comparable to vessel diameter of mesic tree angiosperms. The vessels of G. gnemon var. tenerum (Fig. 3) are distinctively narrow, less than half the average diameter of vessels in the species as a whole. Vessels in G. gneinon are nearly circular in outline, not markedly angular (with each vessel face associated with an adjacent cell) in the sense that vessels of primitive angiosperm families (e.g. Cercidiphyllaceae, Illiciaceae) are angular. Vessel density (Table I, column 3) is inversely correlated with vessel diameter in many dicotyledonous woods. The data of Table 1 show the greatest density for the collection with the narrowest vessels, 0. gnemon var. tenerum (Fig. 2; compare with Figs 3, 5, 7 and 8. In G. gnemon var. gemon, however, there are wide deviations from a straight line relationship. Vessel element length (Table 1, column 4) is relatively uniform for the genus __

GNETUM GNEMOJ’/ WOOD AND BARK 207

- 4 Figures 1 4. Wood sections of Gnetum gnemon. Figs 1, 2. G. gnemon var. gnenson, Aw- 12369. Fig. I. Transverse section; vessels are notably wide in diameter. Fig. 2. Tangential section; axial parenchyma stand walls seen on vessel in centre; septa in fibre-tracheids may be seen between the vessel and the ray at left. Figs 3, 4. Wood sections of G. gneinon var. tenerum, Aw-l2395. Fig. 3. TS; vessels are notably narrow. Fig. 4. Tangential section; upright cells occur in uniseriate rays and occasionally in multiseriate rays. All Figures to same scale as in Fig. 1 whrr divisions = 10 pm. ___

208 S. CARLQUIST

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Figures 5—8. Wood sectioos of G. gnemsn var. gnonon, Garlqsssl 8088, Figs 5, 6. Wood of youog stem. Fig. 5. T.S.; growth riogs are absent. Fig. 6. Uniseriate aod moderately wide multiseriatc rays are present. Figs 7, 8. Wood of root. Fig. 7. T.S. outer portioo of root; narrower imperforate tracheary elements, ceotre, demarcate a growth riog. Fig. 8. TS centre of root; wood begins with wide vessels, changes to oarrow vessels (above). All figures to same scale as io Fig. 1. GJVETUM G]’fEMO11 WOOD AND BARK 209 (range: 1029—1389 jim) compared with the wide range seen in vessel diameters. Although the shortest vessel elements are in G. gnemon var. tenerum, they are not much shorter than those of other collections. Vessel wall thickness differences are evident both in the quantitative data (Table 1, column 5) and in the photomicrographs. The vessel walls of G. nemon var. tenerum (Fig. 3) are less than half the thickness of those of G. gnemon var. gnemon, Cariquist 8088 (Fig. 10) and those of the collection Aw-12369 (Fig. 9). The thinness of vessel walls, combined with wide vessel diameter, makes vessels collapse during sectioning on a sliding microtome. Perforation plates are composed of circular perforations with wide borders (Figs 13—17). Foraminate perforations resemble, but are larger than, the circular bordered pits on lateral walls of vessels and on tracheids (Figs 15, 16). When coalesced to various degrees into fewer perforations, the perforation plate departs from foraminate in accordance with the degree of coalescence (Figs 13—17). Greguss (1955) figured foraminate perforations, but erroneously termed them scalariform in vessels of G. gnelnon. The radial section of Figure 13 shows two perforation plates, The one at left shows a single series of 12 nearly circular perforations, each of which is prominently bordered (five of these perforations, enlarged, are shown in Figure 15). Note that the perforations are more than twice the size of lateral wall pitting in vessels (Fig. 13, upper left, lower right). The borders on these perforations are more prominent than those in vessels of Ephedra (Carlquist, 1989, 1992). Produced by the same fusiform cambial initial as the vessel element at the left of Figure 13 is another at the extreme right in Figure 13. This perforation plate, shown enlarged in Figure 14, contains perforations, the uppermost of which suggests coalescence of two circular perforations. In Figure 16 is a perforation plate, circular in outline, which consists of nine perforations. All are circular except for the uppermost, which suggests coalescence of a pair of perforations. The perforation plate of Figure 17 consists of four well-bordered perforations. The outline of these perforations is basically circular, but altered by their crowding. In all of the specimens except for the young stem and basal older stem (Cariquist 8088) of G. gnemon var. gnelnon, more than half of the perforation plates are simple. A simple perforation plate is shown in Figure 20. The low number of perforations per perforation plate in roots of Carlquist 8088 as compared with stems is notable. Abundance of simple perforation plates explains the low number of perforations per perforation plate (Table 1, column 6). Simple perforation plates are more common in wider vessels, compound perforations are more frequent in narrower vessels. No vesturing was seen on perforation plates. Lateral wall pitting of vessels consists of circular bordered pits, the diameters of which are shown in Table 1, column 7. The circular shape of these is clear in all cases, and is well illustrated in Figure 21. All lateral wall pits have elliptical (Figs 18, 19, 21) to oval (Fig. 20) apertures that are heavily vestured (Figs 18, 19, 21). These vestures are not on the insides of pit cavities (Fig. 21). The vestures appear as extensions of the pit borders. Tori were not observed in lateral wall pits of vessels in G. gnemon, but they definitely do occur in pits of tracheary elements of other species of Gnetum (unpublished data; study currently in progress). The inner surfaces of vessels of G. gnemon, as seen with SEM, range from smooth (Figs 18, 20) to striate (Fig. 19). 210 S. CARLQUTST

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Figures 9—12. Wood sections of 0. gnenon var. gnesnon. Fig. 9. TS, Aw-12369; axial parenchyma is vasicentric (thinnest walled cells adjacent to vessels). Figs 10, 11. Oarlquist 8088, root; Fig. 10. J5 starch ;grey, with dark grey hila) evident in axial parenchvma, fibre-tracheids and ray cells. Fig. 11. RLS; tracheid in centre, starch-filled fibre-tracheids on either side. Fig. 12. Tangential section, Aw-12369; sciereids containing crystals in central portion of ray. All figures except 11 to same scale as in Fig. 9 where divisions = 10 pm; Fig. ii, divisions = 10 pm. G,AIETUM GWEMOJV WOOD AND BARK 211

Figures 1 3— 17. Sections of vessels in Gnetum aemsn var. ne,non Fig. 13. Portion of R.W.S., Aw 12369, to show two perforation plates, extreme left and right, plus lateral wall pitting. Fig. 14. Perforation plate shown at right in Fig. 1 3, enlarged, illustrating coalescence of perforations. Fig. 13. Perforation plate shown at left in Fig. 13, enlarged. to show file of perforations with wide borders. Figs 16, 17. SEM photographs of perforation plates from radial section of young stem, Carlquist 8088. Fig. 16. Perforation plate with more numerous circular perforations. Fig. 17. Perforation plate with four perforations; upper two perforations with one wall only, showing extent of borders. Fig. 13 to same scale as Fig. 9; Figs 14, 15 to same scale as Fig. 11; Figs 16. 17, scale bars = 1 pm. 212 S. CARLQUIST

Figures 18—21. SEM photographs of vessel portions from radial section of C. gnetnon var. gnenssn, Garlquot 8088, stem. Fig. 18. Pit apertures of lateral wall pits, to show’ vcsturiisg. Fig. 19. Striate vessel wall tcxturc, vestured pit apertures of lateral wall pits. Fig. 20. A simple pcrforation plate, plus vestured lateral wall pits. Fig. 21. Lateral wall pitting of vessel, seen from outer surface of one vessel wall; nature of vesturing as seen from the pit cavities evident. Scale bars = 1 p.m. GJvETU’i GIVEMOY WOOD AND BARK 213 Impeiforate tracheay elements and axial parenchjnza Although only tracheids are reported by most authors as the imperforate tracheary elements of Gnetum gnemon, septate fibre-tracheids are present, as reported earlier (Greguss, 1955; Cariquist, 1989). Tracheids, fibre-tracheids and axial parenchyma can be differentiated as follows: Tracheids: walls lignified, about 5 urn thick (Table 2, column 3); pits markedly bordered, pit cavity diameter about 10 im (Table 2, column 4), pit apertures narrowly elliptical, vestigially vestured; septa absent, contents lacking. Fibre-tracheids: walls lignified, about 2.5 Im thick; pits bordered to a lesser extent than in tracheids, pit cavity diameter 4.8 uim; pit apertures narrowly elliptical often elongated by splitting of the wall), nonvestured; septa usually one per fibre-tracheid, thin, nonlignified; starch present (clearly in liquid- preserved samples, but starch remnants variously present in wood samples that have been preserved by drying); fibre-tracheids about as abundant as tracheids, and distributed with them in a nearly random mixture. Axzal parenclyma: walls lignified, about 1.2 im thick, walls tending to be thicker in diffuse than in vasicentric axial parenchyma; pits simple, circular; cells in strands of 4—10, chiefly 5—6, each of the cells surrounded by a lignified secondary wall; starch present (more easily demonstrable in liquid-preserved than in dried material); some axial parenchyma present diffusely, but diffuse cells very rare to moderately rare, the vasicentric axial parenchyma much more abundant (diffuse cells less common in young stems e.g. Carlquist 8088, most common in larger stems, e.g. PRFw-l98l4). Tracheids and fibre-tracheids have been combined for measurement of length (Table 2, column 1) because separation of these two cell types in macerations is difficult and preliminary study showed no appreciable difference between the two cell classes in length. Likewise, tracheids and fibre-tracheids have been combined for determination of diameter, which is outside diameter rather than lumen diameter (Table 2, column 2). A feature of signal importance where the tracheids and fibre-tracheids are concerned is their distribution with respect to each other; this is approximately random, as noted above. In angiosperms, where these cell types coexist in the same wood, the tracheids are always vasicentric, or else they are found in bands in latewood, and termed vascular tracheids (Carlquist, 1988). Where fibre-tracheids are most abundant in G. gnemon, they may be aggregated into tangential groupings (‘diffuse-in-aggregates’) mildly reminiscent of prominent tangential lines of fibre-tracheids in the wood of Ephedra (Cariquist, 1989, 1992). Minimal vesturing on pit apertures of tracheids of G. gnemon was figured by Parameswaran and Liese (1974) and is also shown here (Fig. 23). Pit apertures of fibre-tracheids and tracheids are narrowly elliptical (Figs 22, 23). The extension of pit apertures of imperforate tracheary elements in G. gnemon by means of splits in the wall may be related to formation of reaction wood, and possibly to some extent by the drying of the wood samples.

Rajs Rays are both multiseriate and uniseriate (Figs 2, 4, 6). The multiseriate and uniseriate rays are composed almost exclusively of procumbent cells. Upright 214 S. CARLQUIST

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C.. Figures 22—25. SEM photographs of portioos of a taogcntial section, Garlquiss 8088. Fig. 22. Portions of fibre-rachcids. septa in cell at left; elliptical nature of pit apertures evident. Fig. 23. Portion of a tracheid, to show a vestigially vestured pit aperture. Fig. 24. Axial parenchynia cell with starch grasns, centre. Fig. 25. Portion of ray (right half of photograph) and adjacent fihre tracheids filled with starch grains. Scale bars = 1 pm. GJVKTUM GJVEMOIV WOOD AND BARK 215 or square cells are very infrequently present; where present, these are sheath or tip cells on multiseriate rays, or are located in uniseriate rays (Figs 2, 4, 6). The scarcity of square or upright ray cells in G. gnemon is illustrated in Figure 12, in which essentially all of the cells shown would be procumbent if viewed in radial section. Square or upright cells are only moderately rare in smaller stems, such as that of G. gnemon var. tenerum (Fig. 4). Decreased production of upright and square cells as a stem increases in diameter (the result of horizontal subdivision of ray initials) is a familiar phenomenon in angiosperms and occurs in gymnosperms other than Gnetales (Greguss, 1955). Multiseriate ray height is shown in Table 2, column 6. Although the mean height of multiseriate rays for the species is close to the height of imperforate tracheary elements, some multiseriate rays are very high, over 5 mm. Uniseriate rays are much shorter (Table 2, column 7). The size of multiseriate rays is indicated by the figures on mean width in cell number (Table 2, column 8). Taller multiseriate rays are often more than eight cells wide (Figs 2, 6, 12). Ray cell walls are lignified. In a few multiseriate rays, occasional sclereids or groups of sclereids occur (Fig. 12). Ray cells that are not sciereids mostly have walls about 2.5 jim thick. Greguss (1955) stated that all pits in ray cells are simple in G. gnelnon, but tangential walls of ray cells in this species invariably bear bordered pits. Bordered pits are also common on tangential walls of dicotyledon rays, but often are not reported because investigators are accustomed to looking for borders as seen in face view, whereas ray cell pits are best demonstrated in sectional view in radial sections. Ray cells are filled with starch in liquid-preserved specimens of G. gnemon (Fig. 25, right half of photograph). Wood samples that have been dried as a method of preservation often have only clumped remnants of starch grains when boiled prior to sectioning.

Cystats Rhomboidal crystals are common in ray cells of all collections of the species (Figs 12, 26—28). Crystals were also observed, infrequently, in axial parenchyma of G. gnemon var. tenerum. Occasional paired crystals were observed (Fig. 28). Greguss (1955) claims that druses may be present in ray cells of G. gnemon, but I saw no evidence of them. Crystals in G. gnemon show a great range in size (Figs 26, 27), and crystals may be borne singly, or in combination with smaller crystals.

Growth rings Absence of growth rings is claimed for wood of Gnetum by Martens (1971), but Greguss (1955) reports inconspicuous growth rings. Fluctuation in radial diameter of imperforate tracheary elements can be seen in roots of G. gnemon (Fig. 7). Fluctuation in vessel diameter in relation to growth rings was also observed in the root of G. gnelnon. The root studied was a surface root, so that fluctuation in water availability may have been more pronounced than in a deep root. In the centre of this root, vessels are wider (Fig. 8), but are succeeded by smaller vessels (Fig. 8, top; Fig. 7).

9. in as Fig. scale 30 same 1; Fig. Fig in as scale

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29 Fig.

1 pm; scale bars 26--28 = Figs fibres. gelatinous parenchyma; cortical inner containing

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brachysclercids; parenehyma; cortical Outer crystal-bearing phellem, bottom), top to (from

showing

bark, of

two-thirds 30. Outer Fig. (bottom). xylem secondary to (top) periderm from tissues

show

photograph LP 29. Fig. Aw-12395. 0. tenerum, var. gnemon from bark TS 30. 29. Figs

cell.

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ray crystal Double 28. Fig. ray cells. from crystals (below) very small and Small 27.

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Larger 26. Fig. 8088. Garlquist gnernon, G. gneinon of var. section radial from cells, ray

of crystals photographs SEM 26—28. Figs bark. and wood of gnemoa 0. Sections 26—30. Figures

‘29

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CARLQUIST S.

216 ___ GJvETUM GJvEMW WOOD AND BARK 217 Bark anatomy and variant cambial activity

A young bark formation is shown for G. gnemon var. tenerum (Fig. 29). A periderm composed of numerous layers of phellem but with no apparent phelloderm formation (other than a single layer) is present (Fig. 30). Beneath the periderm of the bark (Fig. 29) are layers of still intact cortex. These cortex layers show radial divisions that probably permit these cells to keep pace with increase in circumference of the stem. These cortical cells contain numerous crystals. A central zone of cortex is converted into a band of brachsclereids (Figs 29, 30). These brachysciereids are extraordinarily thick walled, variously shaped, and frequently with a single encapsulated rhomboidal crystal. The inner portion of the bark (Fig. 29, bottom shows a small amount of secondary xylem beneath the cambium and secondary phloem) consists of secondary phloem. In the secondary phloem, one can see gelatinous fibres (Fig. 30, bottom). These gelatinous secondary walls shrink from the primary walls formed by these fibres. Older bark of G. gneinon var. gnemon shows much the same features but with additions. This particular bark sample comes from a basal stem sample on a flange of the stem—perhaps an incipient buttress. Successive periderms are evident (Fig. 31, top). From proliferation of parenchyma that is interior to the periderm, nests of brachysclereids form (Fig. 31, dark patches). Most of these brachysclereids each contain a large crystal. Parenchyma surrounding these brachysclereid nests as well as secondary phloem parenchyma is rich in starch (Fig. 32, bottom). The production of secondary phloem fibres is extensive (Fig. 33). In the bark of the G. gnemon var. gnemon basal stem flange, the beginnings of new vascular tissue produced by cambia formed from bark parenchyma were observed (Fig. 34). These cambia are oriented at right angles to the main cambiurn of the stem. Such cambia are, very likely, the source of the vascular tissue outside the main woody cylinder reported by Rao & Keng (1975) for G. gnemon. These authors say: “since the periderm is continuous and intact, it is clear that the additional arch-like outgrowths must have originated from superfluous cambia differentiated in the parenchyma tissue”. This accords with my observations. Rao & Keng (1975) make the point that in contrast with the concentric rings of vascular tissues in stems of lianoid Gnetum species, in the old stems of G. gnemon stems they studied, the additional strands of vascular tissue are “arch-like, arranged next to each other, but not showing any concentric arrangement”. Rao & Keng (1975) rightly contrast this feature of the C. gnemon stem, as well as the massiveness of its central woody cylinder, with conditions seen in the lianoid species of Gnetum. In lianoid species of Gnetum, the first vascular cylinder is rapidly completed, and the vast bulk of an older lianoid Gnetum stem is vascular tissue formed by successive cambia rather than by the first vascular cambium. One would like to know, in the case of the G. gnemon tree base reported by Rao & Keng (1975), how the xylem and phloem of the new vascular tissues are connected with those of the central cylinder.

CONCLUSIONS The fact that G. gnemon can produce successive cambia, admittedly in a pattern not identical with that of the lianoid Gnetum species, does provide a 218 S. CARLQUIST

LZ1 -t

Figures 3 1—34. Sections of bark from basal flange of tree trunk of G. gstemsn var. german, GoIqutst 8088. Fig. 3 1. Outer portion of park, showing (top) successive periderms and (below) brachysriercids (dark). Fig. 32. Crystal-containing braehyselereids (top) and starch-rich parenehyma (bottom) from central portion of bark. Fig. 33. Gelatinous fibres from secondary phloem, inner portion of bark (dark). Ftg. 34. Vascular strand onginating from a cambium eambium at right angles to eambium of main cylinder) in the central portion of the bark. Figs 31, 33, 34, scale as in Fig. 1; Fig. 32, scale as in Fig. 9). G.NETUM (LNEAI(W WOOD AND BARK 219 link between subgenus Gnetwn and the other subgenera. The delay, in G. gnemon, in development of supplementary vascular tissues is interesting, and may correlate with the arboreal habit of the species. Before deciding whether the tree habit or the liana habit is ancestral in Gnetum. one would like more information perhaps molecular data may prove decisive. A distinction between subgenus Gnetum and the lianoid species is the presence of septate fibre-tracheids in G. 7zemon, as opposed to their absence in the lianoid species. The lignified secondary walls of the fibre-tracheids theoretically provide increased mechanical strength, while also providing a site for starch storage. This starch storage presumably is related to seasonal growth events. This cell type provides a point of resemblance between Gnetum and Ephedra, which has nonseptate nucleated fibre-tracheids (Cariquist, 1989, 1991). The presence of fibre-tracheids in Ephedra may be related to the mechanically strong stems of Ephedra, many species of which are small shrubs or subshrubs, but some species of which are large shrubs. The impact of wood data on ideas concerning relationships of Gnetales is beyond the scope of this paper. However, examination of wood data given above are basic to such comparisons. Gnetum gnemon is one of two species utilized by Muhammad & Sattler (1982) in their comparisons with wood of selected angiosperms. They claimed to show resemblances in perforation plates, as well as in other vessel features, between the vessels of Gnetwn and those of certain angiosperms. In my opinion, G. gneinon cannot be said to have scalariform or even ‘scalaroid’ perforation plates. When the perforation plates of G. nernon are viewed in a broad sampling instead of as a few selected perforation plates, the conclusion is inescapable that the perforation plates of Gneturn are foraminate, composed of circular perforations (modified in shape where perforation coalescence occurs). The foraminate perforations are markedly bordered (perforations in Ephediri are less bordered). The full range of tracheary element expressions in Gnetum will he reviewed in the terminal paper in this series, but the data in the present paper support the views of Bailey (1925, 1944. 1949, 1953) and Thompson (1918, 1923) concerning the nature of the gnetalean vessel. Also of interest in this connection is that although the vessels of primitive angiosperms are angular in transectional view, often corresponding to scalariforn-i or transitional lateral wall pitting (the horizontal length of pits limited by the wall face), the vessels of Gnetum (as well as those of Ephedra) are circular in transectional view (the pitting not related to wall faces of angular vessels as in primitive angiosperms). Simple perforation plates are more common in wider vessels of G. gnemon, multiperforate plates more common in narrower vessels. This supports the idea, widely held with regard to angiosperm vessels, that evolutionary simplification of the perforation plate is a response to accommodate greater rates of flow. The fact that perforations in G. gnemon are larger than lateral wall pits of vessels would also support that concept. Simple perforation plates are also more common in the roots than in the stems studied. The presence of vestures on pits of vessels and tracheids as contrasted to their absence on pits of fibre-tracheids accords with the concept that vessels and tracheids in Gnetum are conductive cells, whereas fibre-tracheids are not (Carlquist, 1984). Vesturing on pits in Gnetum is adjacent to the pit aperture, and is not present facing the pit cavity. This tends to lend support to the 220 S. CARLQUIST alternative hypothesis that vestures may retard embolism formation by increasing bonding of wall surface with water (Carlquist, 1988) rather than the idea of Zweypfenning (1978) that vestures face the pit membrane and thereby prevent excessive deflection of the pit membrane when pressures on the two sides of the membrane differ markedly. The significance of vestures in Gnetum in relation to ecological and phylogenetic distribution of these structures in other genera will be reviewed in the concluding paper of this series. Tracheids and fibre-tracheids of Gnetum gnernon are about equally common in any given wood sample (fibre-tracheids somewhat more common in structures with a more prominent storage function, such as roots). The two cell types are apparently distributed at random to each other, a fact that places them in distinction to angiosperm woods, in which vasientric tracheids and fibre-tracheids (or libriform fibres) coexist; in these angiosperms, the tracheids are invariably vasicentric, as the term implies, and the fibre tracheids or libriform fibres distal to vessels. Axial parenchyma is diffuse in distribution in primitive angiosperms, but in G. gnemon, the axial parenchyma distribution of which has not been hitherto been analyzed, axial parenchyma is vasicentric, with only a very few diffuse cells in some samples only. The presence of starchrich vasicentric parenchyma around vessels may relate to seasonal activities, perhaps indicating shunting of sugars into vessels to accelerate conduction, in line with the ideas of Sauter (1966a, l966h) and Braun (1970, 1983) that addition of sugars to the sap of vessels can seasonally renew conduction. The presence of growth rings in some specimens of G. gnemon also underlines the possibility of seasonal events in G. gnemon. Quantitative data show that the vessels of G. gnernon var. tenerum are appreciably narrower and more numerous per mm2 of transection than in G. gnemon var. gnemon. This would accord with tendency for trees, which tap larger sources of water, to have generally wider vessels than shrubs (Carlquist, 1988).

REFERENCES

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