IAWA Journal, Vol. 14 (2),1993: 191-204 STRUCTURE OF STEM AND CAMBIAL VARIANT IN SPATHOLOBUS ROXBURGIill (LEGUMINOSAE) by M.N.B. Nair Department of Botany, University of Delhi, Delhi 110 007, India Summary The stern of Spath%bus roxburghii, a Fisher 1989; Ursem & ter Welle 1992). How­ tropicalliana, has alternating layers of xylem ever, they have also been reported in plants and phloem as a result of formation and activ­ with different habits and habitats (Metcalfe & ity of successive cambia. Successive cambial Chalk 1950, 1983; Fahn & Shchori 1967; rings are developed by dedifferentiation of Wheat 1977, Mikesell 1979; Bailey 1980; groups of parenchyma cells outside the dis­ Carlquist 1988; Nair & Mohan Ram 1990). continuous band of sclereid-fibres. The scle­ The large body of information available on reid-fibre band is formed by the development cambial variants is based on mature stern of sclereids between the primary bark fibres. structure. As very few developmental studies Each successive cambium first produces a have been made to trace the precise manner layer of sclereid-fibres which separates the of initiation of these cambia, the interpretation vascular tissue produced by one cambial ring of their end products becomes problematic from the other. After secondary growth, the (Philipson & Ward 1965). epidermis is replaced by periderm. In the old­ Spath%bus roxburghii (syn. Butea parvi­ er stern phelloderm contributes to the forma­ flora Roxb.) (family Leguminosae) is a gigan­ tion of new cambiallayers. Secondary phloem tic climber that twines around trunks of trees has sieve tube members; companion cells, in Indian sal and teak forests (Fig. 1) and caus­ phloem parenchyma, phloem fibres and se­ es much damage. It attains a diameter of up to cretory cells. The wood shows a tendency I m. The stern yields a red gum that resem­ towards ring-porosity only in the first xy­ bles 'kino' of commerce extracted from Pte­ lem layer. The subsequent layers are diffuse­ rocarpus marsupium (Gamble 1902). porous. The vessels are wide and narrow. The anomalous stern structure in Spatho­ Perforated ray cells or radial vessels are fre­ /obus roxburghii Benth. has been briefly re­ quent in the wood and probably help in ver­ ported earlier (Gamble 1902; Solereder 1908; tical conduction by interconnecting vessel Metcalfe & Chalk 1950). However, no detail­ endings. In this scandent species parenchyma ed study of the cambial variant and structure cells are abundant. It is inferred that they help of the secondary xylem has been done previ­ the vessel segments to remain undamaged ously in this species. when the woody stern twists around sup­ ports. Materials and Methods Key words: Cambial variant, Leguminosae, The sampies for investigation were col­ liana, perforated ray cells, Spath%bus, lected from Cheenikkala (Tropical forest) of successive cambia, vestured pits. Nedumangad forest area, Kerala State, India. Portions of stern of varying diameter (1 to 12 Introduction cm) were collected and fixed in F AA (forma­ Cambial variants (anomalous secondary lin : acetic acid : 50% ethanol = 1 : 1 : 8) and growth) are of common occurrence in tropical evacuated until they sank in the fixative. They lianas and vines (Basson & Bierhost 1967; were sectioned on a sliding microtome, stain­ Dobbins 1969, 1971, 1981; Dobbins & Fisher ed with 0.05% toluidine blue 0 in 0.1 M phos­ 1986; Carlquist 1985, 1988, 1991; Ewers & phate buffer pH 6.8 (O'Brien et al. 1964), Downloaded from Brill.com09/29/2021 04:58:37PM via free access 192 IAWA Journal, Vol. 14 (2),1993 Table 1. Wood characteristics in Spatholobus roxburghii. S.D. Mean diameter of larger vessels (width 100 ~m and above) 322.0 ~m* 57.5 Mean length of the larger vesseI element (width 100 ~m or above) 324.0 ~m* 105.96 Mean diameter of narrow vessels (width below 100 ~m) 56.8 ~m* 15.8 Mean length of the narrow vessel elements (width below 100 ~m) 392.0 ~m* 93.1 Frequency of vesseIs/mm2 (wide) 4.9 1.9 Frequency of vessels/mm2 (narrow) 29.7* 7.3 Mean diameter of pits on the vessel element wall 10.8 ~m* 0.9 Maximum ray height 186 cells Maximum ray width 7 cells Mean diameter of the stern at the time of initiation of first 2.67 cm** 0.23 additional cambium Mean thickness of the phloem layer 1.9 mm** 0.27 Mean thickness of the xylem layer IOmm** * = average of 60 readings; ** = average of 20 readings. safranin 0 alone, and with safranin 0 and fast phloem rays and secretory cells (Figs. 5, 7). green FCF (Berlyn & Miksche 1976). Mate­ In older bark the phloem has several tangen­ rials were prepared for scanning electron mi­ tially arranged groups of secondary phloem croscopy as described earlier (Nair 1987). fibres (Figs. 5-7). Phloem rays show limited Measurements were taken using a calibrated dilation growth towards the outside (Fig. 5). eyepiece micrometer (Table 1). The presence The sieve tube members usually collapse in of heartwood was tested by TTC (2,3,5-tri­ the previous year's phloem (Figs. 5,6). Sev­ phenyl tetrazolium chloride) (Fahn & Amone eral secretory cells are present in the secondary 1963). PAS reaction was carried out accord­ phloem (Figs. 5, 7, 11, 12). They develop ing to the method suggested by Jensen (1962). from the cambium and can be distinguished even in the early stages of deveIopment. Results These cells contain insoluble polysaccharides The woody stern of Spatholobus rox­ (Fig. 10) as confirmed by PAS reagent. As burghii has alternating layers of xylem and secondary growth proceeds, the periderm phloem (Figs. 2, 40a, b, d). The mean thick­ replaces the epidermis. Sc1ereids or sc1ereid ness of the phloem layer is 1.9 rum (Table 1). groups develop in the cortex (Fig. 14). Rhyti­ Each phloem layer is accompanied by cam­ dome is present in the old bark (Fig. 15). bium internally (Fig. 3). The cambium asso­ ciated with old inner phloem layer shows de­ Development 0/ cambial variant generation at certain regions (Fig. 4). Initially the secondary growth in Spatho­ lobus roxburghii is normal. However, initi­ Structure 0/ bark ation of an additional cambium occurs by The secondary phloem consists of sieve dedifferentiation of a few cortical parenchy­ tube members (Figs. 8, 9), companion cells ma cells peripheral to the tangential band of (Fig. 8), secondary phloem fibres (Figs. 6, 7), axial phloem parenchyma cells, multiseriate (text continued on page 200) Downloaded from Brill.com09/29/2021 04:58:37PM via free access Nair - Cambial variant in Spatholobus 193 Legend 0/ Figures 1-39 (pages 4-9): Fig. 1. The seandent habit of Spatholobus roxburghii (arrow). - Fig. 2. Transverse seetion (TS) of stern showing alternating layers of xylem and phloem. Arrow indieates the selereid-fibre layer. Seale bar = 355 ~m. - Fig. 3. Magnified view of portion of TS of stern depicting addi­ tional eambium and its derivatives. Seale bar = 130 ~m. - Fig. 4. TS of stern showing degen­ eration of portion of old eambium. Seale bar = 130 ~m. Figs. 5 & 6. Portion of TS of seeondary phloem showing erushed sieve tube members, phloem parenehyma, seeondary phloem fibres and phloem rays. Seale bar for 5 = 330 ~m; for 6 = 105 ~m. - Fig. 7 . TS of stern showing seeondary phloem with seeretory eells (arrow). Seale bar = 130 ~m. - Fig. 8. TS of portion of eambium and eurrent years phloem showing sieve tube mem­ bers and eompanion eells. Seale bar = 36 ~m. - Fig. 9. Longitudinal seetion: surfaee view of lateral wall of a sieve tube member showing sieve areas. Seale bar = 24 ~m. - Fig. 10. Devel­ oping seeretory eells showing PAS positive eontents. Seale bar = 67 ~m. - Fig. 11. TS of phloem showing a group of seeretory eells. Seale bar = 75 ~m. - Fig. 12. LS of portion of seeondary phloem showing seeretory eells. Arrows indieate the darldy stained gum in the seere­ tory eells. Seale bar = 285 ~. - Fig. 13. Portion of bark showing the tangential selereid-fibre layer (arrow) and site of initiation of additional eambium. Seale bar = 130 ~m. Fig. 14. Portion ofthe TS ofbark showing sclereids. (arrows). Seale bar = 145 ~. - Fig. 15. Portion of old bark showing part of seeondary phloem, periderm and rhytidome. Seale bar = 265 ~m. - Fig. 16. TS of the old bark showing phelloderm giving rise to additional eambial layer. Seale bar = 105 ~m. - Figs. 17 & 18. TS of stern showing initiation of additional eam­ bium outside the sclereid-fibre layer. Seale bar for 17 = 250 ~m; for 18 = 125 ~m. - Fig. 19. LS of portion of the newly formed additional eambium. Seale bar = 22 ~m. - Figs. 20 & 21. TS of stern showing vaseular tissue produeed from the additional eambium. The sclereid-fibre layer (arrows) separates the newly formed vaseular tissue from the previous one. Seale bar for 20 = 315 ~m; for 21 = 357~. - Fig. 22. LS ofthe stern showing the diseontinuous sclereid­ fibre layer. Seale bar = 165 ~m. Figs. 23 & 24. Longitudinal seetion of the sclereid-fibre layer. Figure 23 shows only selereids and figure 24 shows fibres and sclereids. Seale bar for 23 = 55 ~m; for 24 = 105 ~m. - Fig. 25. Portion of TS of stern showing tendeney for ring porosity in the first xylem layer. Seale bar = 250 ~m. - Fig. 26. TS of wood showing vessel dimorphism. Seale bar = 250 ~m. Fig. 27. Vestured intervessel pits in narrow vessel, viewed from outside the vessel. Seale bar = 7 ~m. - Fig. 28. Vestured intervessel pits of wide vessel, viewed from outside the vessel. Seale bar = 3.3 ~m. - Fig. 29. Sealariform intervessel pits near the end of the vessel element, view­ ed from outside the vessel. Seale bar = 7 ~m. - Fig. 30. Vestured intervessel pits, viewed from inside the vessel.