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IAWA Bulletin Ns, Vol. 1 (3),1980 133 WOOD and BARK

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IAWA Bulletin Ns, Vol. 1 (3),1980 133 WOOD and BARK IAWA Bulletin n.s., Vol. 1 (3),1980 133 WOOD AND BARK ANATOMY OF ALLUAUDIA (DIDIEREACEAE) 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 Alluaudia ascendens 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 species 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. 134 IAWA Bulletin n.s., Vol. 1(3),1980 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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