IAWA Bulletin n.s., Vol. 1 (3),1980 133

WOOD AND BARK ANATOMY OF () FROM MADAGASCAR

by

R.W. den Outer and W. L. H. van Veenendaal Department of Botany, Agricultural University, Wageningen, The Netherlands

Summary The anatomy of the secondary phloem and south of Tulear) is a shrub, 2 m heigh, a stem xylem of the tree Drake diameter of 4 cm and about 15 growth rings has been compared with that of Alluaudia near the stem base. Anatomical features were humbertii Choux, both belonging to the studied in transverse, radial and tangential endemic family Didiereaceae of Madagascar. sections and macerations. All sections were The differences between the two are embedded in Kaiser's gelatin-glycerin (Johan­ small. In contrast with A. humbertii the cortex sen, 1940). Means and ranges of the length of of A. ascendens, persistent during the lifetime sieve-tube members, vessel members, parenchy­ of the tree, is thick and possesses a network of ma strands, fibre-sclereids, fibrous elements vascular bundles. These bundles are in con­ and the radial vessel diameter are based on at nection with the vertical system of the stem least twenty-five individual measurements. The via the horizontal ray system in non-conduc­ sieve-tube type and companion-cell type were ting and conducting secondary phloem and classified according to Zahur (1959). The air secondary xylem. The function of these dried material used for S.E.M. had clean cut bundles is discussed. surfaces, was sputter-coated with gold and observed in a Jeol scanning electron micro­ Introduction scope type U-3. The endemic family Didiereaceae from the dry area of south-west Madagascar, is a small Results one, composed of 4 genera with in all 11 or 12 species. The representatives are trees or shrubs Wood Anatomy somewhat cactus-like in habit with small simple The secondary xylem cylinder of the inves­ leaves or only thorns; they are clearly charac­ tigated Alluaudia ascendens has a diameter of terized by the architecture of the flowers. The about 10 cm. four genera of the family are Decaryia, Alluau­ Growth rings fairly distinct, (0.3-) 1.3 ( - diopsis, Didierea and Alluaudia. Information 2.3) mm (Fig. 5). Growth-ring boundaries are on their wood - and especially bark - anat­ marked by more and larger vessels in the early omy is very scarce. Samples of only two wood, while in the late wood libriform fibres Alluaudia species were at our disposal and used are flattened and the ray cells nearly always for this study. short in radial direction. The greyish-beige wood is rather often semi-ring-porous. Heart­ Materials and Methods wood is not recognizable. Bark and wood samples used are from the Vessels c. 40/mm2, solitary or in radial to Van Veenendaal/Den Outer collection, Mada­ tangential multiples or clusters, round to gascar (1978). The collection is housed at the oval or flattened where in contact with each Department of Botany, Agricultural University, other, radial diameter (40-)100( -200) 101m, Wageningen, The Netherlands. All the material tangential diameter (40-)80( -120) 101m. Walls studied is accompanied by herbarium vouchers. 1.5-2 101m thick. Vessel-memberlength (100-) The samples were collected from stems and im­ 250( -430) 101m. Perforations simple (sometimes mediately fixed in F.A.A. Alluaudia ascendens in pairs) in slightly oblique to horizontal Drake (collection number V. and O. 1129, 10 end walls. Inter-vessel pits alternate, 6-7 km east of Tsihombe) is a tree of 8 m heigh, 101m, sometimes with coalescent apertures. with a dbh of II cm and about 35 growth rings Vessel-ray and vessel-parenchyma pits half­ at the stem base. Alluaudia humbertii Choux bordered to almost simple, 10-25 101m. Vessels (collection number V. and o. 1068, 18 km usually in contact with parenchyma.

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Fig. 1-4. Alluaudia ascendens Drake. Scanning electron micrographs of the secondary xylem. -- I. Transverse and tangential surface, showing a large wood ray with tracheal elements in its centre, x 145. -- 2. Radial surface. Tracheal elements of the vertical system bend towards and make contact with tracheal elements of the wood ray. Note the simple crystals, x ISO. -- 3. Transverse surface, showing tracheal elements in the wood ray. Note the simple perforation in the centre, x 510. -- 4. Transverse surface, showing spiral thickenings in tracheal wood-ray elements and parenchyma cells, x 5240.

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Librifonn fibres (600-)880( -1190) Mm phloem immediately outside the cambial zone long, walls 3 Mm thick (in the late wood (200 Mm), the non-conducting phloem (620 somewhat thicker) with many simple pits with Mm), a cortex (c. II mm) and finally the peri­ slit-like inner apertures mainly confined to the derm (c. 200 Mm). radial walls often in two vertical rows, non­ The axial system on cross section of the septate. Fibre-tracheids and vascular tracheids conducting secondary phloem (Figs. 9 & 10), frequent near the vessels, c. 470 Mm long, dia­ is composed nearly half of sieve tubes and meter 25 Mm. companion cells and about half of parenchyma ParenchYmil paratracheal (usually forming a cells. Fibres (fibre-sc1ereids) are absent or complete sheath of one cell wide around the scarcely present in the transitional zone to the vessels), apotracheally diffuse and marginal non-conducting phloem. (initial). Strands of 2-3 cells, c. 500 Mm Sieve-tubes scattered or in groups of 2 or long. 3 (bast type s or g; Den Outer & Fundter, Rays (4-)6(-9)jmm, 2-3-seriate, usually 1976), diameter c. 22 Mm. Sieve-tube member with short uniseriate tails, composed of erect type II (Zahur, 1959) length (165-)335(-430) (lg 120, rd 80, tg 45 Mm), square (lg 80, rd 80, Mm. Sieve plates compound (c. 4 sieve areas), tg 45 Mm) and a few procumbent cells (lg 70, oblique to horizontal, many starch-like grains rd 120, tg 45 Mm). Width c. 90 Mm, height which do not colour purple when treated with 1100(-2000) Mm. Perforated ray cells rather iodine near the sieve plates (Fig. 11). Sieve often present, perforations up to 50 Mm. areas in radial walls, indistinct, scarce, horizon­ Some rays are much wider, c. 280 Mm (Figs 1 & tal diameter 6 Mm. 7) with in their centre vessels with spiral Companion cells type C (Zahur, 1959), thickenings, vascular tracheids and tracheids 3( -2) cells per strand, oval on cross section, (Figs. 3, 4 & 8) not accompanied by phloem diameter 7-8 Mm. Strands usually situated elements. The horizontally stretched tracheal along one of the radial walls of the sieve-tube elements (length (100-)150(-230) Mm, member. diameter 10-15 Mm) within the rays bend at a ParenchYmil cells round to oval on cross sec­ certain point into a vertical direction, leave the tion or flattened in radial direction, radial ray and become part of the axial system (Figs. and tangential diameter 22-45 Mm, red-brown 2 & 6). to dark brown contents absent (in contrast Crystals in ray parenchyma cells rhomboidal; with the non-conducting phloem). Strands of 2 druses less frequent. cells, length (390-)440( -480) Mm. Rays uniseriate and 3( -2)-seriate with short The secondary xylem of the investigated uniseriate tails, composed of erect and square Alluaudia humbertii differs slightly from that cells (lg 65, rd 65, tg 50 Mm) and a few pro­ of A. ascendens. The following differences cumbent ones. Cell contents red-brown sub­ were observed. stances or druses. Some of the multiseriate rays Growth rings more distinct, (0.2-)0.4( -0.5) are more than 3 cells wide and possess radial mm, diffuse vessel arrangement. All axial ele­ vascular bundles (Figs. 14 & 16). ments are somewhat shorter. Vessels c. 5 2jmm 2, The non-conducting phloem consists of dila­ radial and tangential diameter one fourth tating phloem rays of the TWa-type alter­ smaller, perforations more often in pairs. nated with wedge-shaped areas composed of Walls 2.5-3.5 Mm. Inter-vessel pits more often elements of the axial system. The sieve tubes opposite. Vessels usually in contact with li­ are crushed in these areas. The parenchyma briform fibres. Libriform fibres with simple cells sometimes have red-brown contents. Many pits in one vertical row, walls 5 Mm thick. fibre-sc1ereids are formed, length (350-)410- ParenchYmil mainly diffuse and initial. Rays (-470) Mm, walls thick (7 Mm) in which many 5 jmm, usually 4-seriate, width c. 180 Mm, simple pits with slit-like vertical inner aper­ height c. 1300 Mm, composed of erect (lg 100, tures. rd 45, tg 45 Mm) and square cells (cubical, The cortex is almost entirely composed of 45 Mm wide). Procumbent cells, perforated ray parenchyma cells. Towards the periderm rela­ cells and wide rays with tracheal elements in tively thin-walled sc1ereids are present. Paren­ the centre, absent. Crystals present as sand, chyma cells tangentially stretched (tg 165 Mm) seldom druses, in the ray parenchyma cells. (strong dilatation). Contents rather frequently a large druse or red-brown substances especially Bark Anatomy near the periderm, sometimes dark brown to The bark of the investigated Alluaudia black I!;ranular masses. Some parenchyma cells ascendens is about 12 mm thick. It can be are much larger (diameter c. 240 Mm), relative­ divided into four zones, i.e. the conducting ly thick-walled without any visible contents.

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Fig. 5-10. Alluaudia scandens Drake. Light micrographs. -- 5. Transverse section of the secondary xylem. Note the three growth-ring boundaries, x 30. -- 6. Radial section of the secondary xylem. Tracheal elements of the vertical system bend towards and make contact with tracheal elements of the wood ray, x 95. -- 7. Tangential section of the secondary xylem. A wide wood ray with tracheal elements right at the top of the photograph, x 30. -- 8. Tangential section of a wide wood ray. Detail of Fig. 7, x 200. -- 9. Transverse section of the secondary phloem. From top to bot­ tom: non-conducting phloem with fibres, conducting phloem without fibres, cambial zone and a small part of the secondary xylem, x 67. -- 10. Detail of Fig. 9. From top to bottom: conducting phloem with living sieve-tubes, companion cells and phloem-parenchyma cells ; cambial zone; secondary xylem, x 235.

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The parenchymatous tissue of the cortex is 1975), infonnation about the anatomy of the traversed in all directions by vascular bundles, secondary phloem and xylem of the different which fonn a thin network (Fig. 13) and are species of the family is scarce (Heimsch, 1942; connected with the radially orientated bundles Metcalfe & Chalk, 1950). This situation has in the rays of the non-conducting phloem: been improved since Rauh & Dittmar (1970) Vascular bundles oval in cross section (c. 420 described the anatomy of the axis and thorns by 130 I'm), collateral (Fig. 12). The total of the representatives of the family. Yet phloem part is 130 I'm high, including the cap anatomical investigations on the secondary of crushed sieve elements of 65 I'm high on the phloem but also on the secondary xylem of A. outer side. The phloem is composed of sieve­ ascendens and A. humbertii were absent or tube members with usually simple, horizontal incomplete so far. to slightly oblique sieve plates, companion cells A. ascendens is considered to be derived and phloem parenchyma cells. The xylem part from A. humbertii, i.e. A. ascendens is more is about 280 I'm high and composed of tracheal specialized (Rauh & DittIllilr, 1970). Wood and elements often with simple perforation plates bark anatomical arguments for this statement (vessels) and helical to reticulate thickenings, are scarce, since the differences between the and xylem parenchyma cells. The phloem and two species are not great. Maybe some charac­ xylem parts are connected by means of paren­ teristics of the secondary xylem can be used, chyma cells from the remainder of the procam­ but none at all of the secondary phloem. bium; meristematic activity is lacking. Both The most important difference between the sieve elements, companion cells and tracheal two species is the presence of vascular bundles elements are about 140 I'm long (Fig. IS). The in A. ascendens, which were not observed in A. parenchyma-cell strands or cells when no humbertii. Perforated ray cells occur very often partion walls has been fonned, are some­ in A. ascendens, but are hardly present in A. what longer. humbertii. Periderm in only one layer. The phellem is The perforated ray cells (Chalk & Chatta­ composed of 1-3 cells wide tangential bands way, 1933; Carlquist, 1960) have perforations of thick-walled cells, regularly alternating with in their radial walls, either to vessels of the 3-8 cells wide tangential bands of thin-walled axial system of the stem, to the horizontally cells. All cells are radially flattened. Phe!­ stretched tracheal elements of the vascular lodenn c. 9, cells wide, parenchymatous, but bundles in the rays, or to other ray parenchy­ soon forming sclereids. ma cells. Although they might be intermediate between ray cells and vessel elements in mor­ The following differences were found in the phology (Carlquist, 1961), they are not radial bark of A. humbertii, when compared with A. vessel elements (Van Vliet, 1976) since they do ascendens. not form a radial tube, possess no bordered pits The total thickness of the bark is c. 4.2 and the perforations are restricted to the radial mm, the width of the conducting phloem 120 walls only. /-1m, that of the non-conducting phloem 300 Thorns of the Didiereaceae genera are homo­ /-1m, of the cortex 3.5 mm and the peridenn is logous with leaves (Rauh & Dittmar, 1970), about 225 I'm thick. Fibre-sclereids absent, but not with branches (Perrot & Guerin, 1903). many large druses with a diameter up to 280 Though no connection was found between the I'm are present in the cortex. Near the peridenn network of vascular bundles in the cortex of A. groups of stone cells occur. Sieve-tube member ascendens and the vascular tissue of the thorns, type III (Zahur, 1959), length (165-)220- these vascular bundles might be considered as (-365) I'm, diameter c. 15 /-1m. Sieve plates leaf traces. The phellodenn of especially A. simple, but also two sieve areas per sieve plate. ascendens is composed of many cell layers and Companion cell type C, two cells per strand. has an assimilation function. In the other Parenchyma strands with two cells, length c. Didiereaceae there is only one peridenn layer 350 I'm. Rays c. 4-seriate with short uniseriate originating via the phellogen out of the subepi­ tails, composed of erect and square cells. dennal layer of the axis, except in Alluaudiop­ Vascular bundles absent. sis mamieriana Rauh (Rauh & Dittmar, 1970). Since the assimilation of the leaves (thorns) is Discussion insignificant, this function is taken over for the Although the systematic position of the fam­ greater part by the phelloderm of the long and ily Didiereaceae has been cleared up lately slender stems. Transportation of assimilates (most authors classify the family within the and water from and to this phelloderm is order Centrospennae or : Jen­ probably perfonned by this network of vascu­ sen, 1965; Rauh & Scholch, 1965; Straka, lar bundles in the cortex. Connection with the

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Fig. 11-16. Alluaudia ascendens Drake. Light micrographs. -- II. Tangential section near the cambial zone, showing many starch-like grains near the oblique compound sieve plates of two sieve tubes, x 520. -- 12. Radial section of the cortex, 6.9 mm from the cambial zone, show­ ing a cross section of a vascular bundle. Phloem part at the top, xylem part at the base of the photograph, x 130. -- 13. Radial section of the cortex, 5.3 mm from the cambial zone, showing a vertical, branching, vascular bundle, x 82. -- 14. Tangential section near the cambial zone. Vascular bundle of a wide phloem ray. Phloem part at the top, xylem part in the middle of the photograph, x 140. -- 15. Maceration. Tracheal element with spiral thiCkenings from a vascular bundle of the bark, x 280. -- 16. Transverse section of the non-conducting secondary phloem. Wide phloem ray with a radial vascular bundle in its centre, x 54.

Downloaded from Brill.com09/25/2021 04:54:15PM via free access IAWA Bulletin n.s., Vol. 1 (3), 1980 139 vertical vascular system of the axis, takes place Metcalfe, C.R. & L. Chalk. 1950. Anatomy of via the rays. In the phloem rays the phloem the dicotyledons. Vol. I. Clarendon Press, part of the bundle bends towards a vertical Oxford: 447-448. position and fuses with the secondary phloem; Outer, R.W. den & J.M. Fundter. 1976. The in the wood rays the same happens with the secondary phloem of some Combretaceae xylem part of the bundle, moreover perforated and the systematic position of Strepho­ ray cells are present here. Such a system could nema pseudocola A. Chev. Acta Bot. Neerl. not be found in A. humbertii. 25: 481-493. Perrot, E. & P. Guerin. 1903. Les Didierea de Acknowledgements Madagascar. Historique, morphologie ex­ Our sincere thanks for Mrs. I. van Touw­ terne et interne, developpement. J. Bot. Koeten, who prepared most of the slides used Fr. 17: 223-251. for this study. Furthermore we are most grate­ Rauh, W. & K. Dittmar. 1970. Weitere Unter­ ful to Mrs. R. J. J. R. Groot-Scholte for typing suchungen an Didiereaceen. 3. Verglei­ the manuscript. chend-anatomische Untersuchungen an den Sprossachsen und den Dornen der Didierea­ References ceen. Sitzungsber. Heidelberger Ak. Wiss., Carlquist, S. 1960. Wood anatomy of Astera­ Math.-Naturw. Kl. 1969/70, Abh. 4: 159- ceae (Compositae). Trop. Woods 133: 246. 54-84. -- & H.F. Sch61ch. 1965. Weitere Untersuch­ - 1961. Comparative anatomy. Rine­ ungen an Didiereaceen. 2. Infloreszenz, hart & Winston, New York. bliitenmorphologische und embryologische Chalk, L. & M.M. Chattaway. 1933. Perforated Untersuchungen mit Ausblick auf die syste­ ray cells. Proc. R. Soc. B. 133: 82-92. matische Stellung der Didiereaceen. Sitz. Heimsch, Ch. 1942. Comparative anatomy of ber. Heidelberger Ak. Wiss., Math.-Naturw. the secondary xylem in the 'Gruinales' Kl. 1965, Abh. 3: 221-434. and 'Terebinthales' of Wettstein with ref­ Straka, H. 1975. Palynologie et differentiation erence to taxonomic grouping. Lilloa 8: systematique d'une famille endemique de 83-198. Madagascar: les Didiereacees. Boissiera 24: Jensen, U. 1965. Sereologische Untersuchun­ 245-248. gen zur Frage der systematischen Einord­ Vliet, G.J .C.M. van. 1976. Radial vessels in rays. nung der Didiereaceen. Bot. Jb. 84: 233- IAWA Bull. 1976/3: 35-37. 253. Zahur, S. 1959. Comparative study of second­ Johansen, D.A. 1940. Plant microtechnique. ary phloem of 423 species of woody dico­ McGraw-Hili Company Inc., New York & tyledons belonging to 85 families. Cornell London. 523 pp. Univ. Agr. Exp. St. Mem. 358, 160 pp.

WOOD ANATOMY NEWS

(continued from page 11 0)

New Botany Department in Transkei IAWA Member Dr. C.T. Johnson, senior cates of which will be available on request, lecturer at the newly founded University of preferably in exchange for other botanical Transkei informs us that his department will be materials. To build up a library, the receipt of involved in the compilation of a che.cklist of duplicate journal issues and the like would also native and introduced in Transkei. In highly be appreciated. Dr. Johnson's address: connection with this a herbarium collection Department of Botany, University of Transkei, will be accumulated, and Dr. Johnson intends Private Bag X5092, Umtata, RepUblic of Trans­ to collect wood samples in the process, dupli- kei.

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