IAWA Journal, Vol. 17 (3),1996: 311-318

COMPARATIVE STRUCTURE OF VASCULAR CAMBIUM AND ITS DERIVATIVES IN SOME SPECIES OF STERCULIA by K. S. Rao, Kishore S. Rajput & T. Srinivas Department of Botany, Faculty of Science, Maharaja Sayajirao University of Baroda, Vadodara-390 002, India

SUMMARY

Structural variations in cambium, xylem and phloem collected from main trunks of Sterculia colorata, S. alata, S. villosa, S. urens and S. foetida growing in the South Dangs forests were studied. In all five species, the cambium was storied with variations in the length of fusiform cambial cells. Compared to other species S. foetida had the longest and S. urens the shortest fusiform cambial cells. Cambial rays in all the species were compound (tall) and heterocellular with sheath cells. Their height and width were maximal in S. foetida and in S. villosa respectively. In all the species the storied nature of fusiform cambial cells was maintained in derivative cells that developed into sieve tube elements; vessel elements and axial parenchyma of both phloem and xylem. However, fibres of phloem and xylem were nonstoried. The dimensions of elements in phloem and xylem varied among the species. The variation in the mean length of sieve tube elements and vessel members coincided with that of fusiform cambial cells. Key words: Vascular cambium, phloem, Sterculia.

INTRODUCTION

Structure of cambium differs from species to species with respect to the shape, size, length, width and arrangement of fusiform cambial cells and cambial ray cells. Based on the arrangement of fusiform cambial cells, two types of cambia are recognised, storied and nonstoried. Nonstoried cambium is more prevalent in plants than the storied one (Ghouse & Iqbal 1975; Ghouse & Hashrni 1977; Rao & Dave 1981, 1982; Silva et al. 1990). Hence more information is available on structural and seasonal variations of nonstoried cambium. Occurrence of storied cambium is reported in few tropical genera and considered to be more advanced than the non storied one (Bailey 1923; Paliwal & Prasad 1970; Ghouse & Yunus 1974a, 1974b; Yunus et al. 1978; Rao & Dave 1984). The occurrence and general organisation of the vascular cambium in many tropical tree species remains unknown. It is well known that length and width of cam• bium cells and their derivatives differ by age and height level within the same tree (Furqan & Ahmad 1981; Iqbal & Ghouse 1983; Khan & Kalimullah 1991), but little information is available on the comparative studies on the vascular cambium and its

Downloaded from Brill.com09/25/2021 12:26:30AM via free access 312 IAWA Journal, Vol. 17 (3), 1996

Fig. 1. - A, B, E, F, H = tangential view; C, D, G, I, J = transverse view. - Storied arrangement of fusiform cambial cells in Sterculia colo rata (A), S. alata (B), S. villosa (E), S. urens (F) and S.foetida (H); x 75 (FCC = fusiform cambial cells; RCC = ray cambial cells; arrowhead = sheath cells. - Distribution of axial parenchyma in S. colorata (C), S. villosa (D), S. urens (G), S. alata (I) and S. foetida (J); x 75.

Downloaded from Brill.com09/25/2021 12:26:30AM via free access Rao, Rajput & Srinivas - Cambium of Sterculia 313 derivatives in different species of same genus (Ghouse et al. 1976). The present study is aimed to ascertain the presence of storied cambium in other species of Sterculia in addition to S. urens and S. foetida (Ghouse et al. 1973) and reports the variation of anatomical characteristics of secondary xylem and phloem.

MATERIALS AND METHODS

Samples of cambial tissue together with the outer xylem and inner phloem were col• lected from main trunks at breast height of the trees of Sterculia colo rata, S. alata, S. villosa, S. urens and S. foetida growing in South Dangs, a moist deciduous open forest of Waghai region, Gujarat State (India). Three trees of each species having a more or less similar age (13-15 years) and trunk diameter (45-50 cm) were selected to obtain two blocks from each tree. Samples measuring about 60 x 20 mm were taken using a chisel, hammer and single edge blade and immediately fixed in FAA (Berlyn & Miksche 1976) in the second week of January 1995. Small blocks measuring about 20 x 20 mm were cut from the sampled strips using a hacksaw. Suitably trimmed small pieces of these blocks were sectioned on a Ernst-Wetzlar sliding microtome in transverse and tangential longitudinal planes at a thickness of 12-15 Iilll. These sections were tied to slides with fine cotton thread and stained with tannic acid-ferric chloride-Lacmoid combination (Cheadle et al. 1953). After passing through an ethanol-xylene series they were mounted in DPX. A one mm wide portion of xylem bordering the cambial zone was macerated with Jeffrey's fluid (Berlyn & Miksche 1976) at 55-60D C for 24-36 hours. The average length of fusiform cambial cells, xylem fibres, vessel elements, sieve tube elements and height of cambial rays were calculated from a measurement of 100 elements from each block. Measurement of phloem cells was made directly from the tangentiallongi• tudinal sections. Vessel frequency was counted by using a projection disk mounted on the microscope. Fusiform and cambial ray cell ratio were estimated following the method of Ghouse and Yunus (1974b).

RESULTS

All the species of Sterculia investigated had storied cambium with axially elongated fusiform cambial cells and isodiametric cambial ray cells. In tangential section, fusiform cambial cells were roughly hexagonal while cambial rays were compound with mar• ginal sheath cells (Fig. IF). The radial walls of the fusiform cambial cells were beaded due to the presence of numerous primary pit-fields. These cells underwent radial longitudinal division, re• sulting in two daughter cells of equal size. Although the overall organization of cambial cells was almost the same, the individual cell size, their relative number and propor• tion differed to a considerable extent among all the species. The size of cambial cells varied on average from 302-424 Iilll. Their length was shortest in S. urens (Fig. IF) and longest in S. foetida (Fig. lH).

Downloaded from Brill.com09/25/2021 12:26:30AM via free access 314 IAWA Journal, Vol. 17 (3),1996

2000 - 370

1800 320

1600 270 -

! 1400 ! 220 £ £ ,---- Ol) '0 .0) .~ ..<:: .., 1200 .., 170 0::'" - 0::'" - -

1000 120 -

800 70

0' A B c D E 0' A B c D E

Fig. 2. Histogram showing mean cambial ray Fig. 3. Histogram showing mean width of height (/JIll) in Sterculia colorata (A), s. alata cambial rays (/JIll) in Sterculia colo rata (A), (B), S. villosa (C), S. urens (D), and S.foetida S. alata (B), S. villosa (C), S. urens (D), and (E). S. foetida (E).

Cambial rays were found to be compound, heterocellular with 1-3 layers of marginal sheath cells. Variation in length and width of cambial rays were found to be significant among all the species of Sterculia (Fig. 2 and 3) ranging from 839-20021lill and 131- 3611lill respectively. They were shortest (839 Ilill) in S. foetida (Fig. IH). The ratio of ray and fusiform cambial cells also differed between the different spe• cies investigated. Fusiform cambial cells constituted 60% of the tangential area in S. colorata, 56% in S. alata, 61 % in S. villosa, 61 % in S. urens, and 55% in S. foetida. The secondary phloem in all the species of Sterculia consisted of sieve tube mem• bers, companion cells, axial and ray parenchyma cells and fibres. In transverse section phloem fibres appeared in more or less continuous tangential bands interrupted by rays except in S. alata where they were irregularly scattered among sieve tube members. Sieve tube members were the largest cells in transverse section. Companion cells oc• curring at the margins of sieve tube members were the smallest cells in transverse section. The axial parenchyma cells were intermediate in size between sieve tube members and companion cells and were often associated with bands of phloem fibres. They formed alternating bands of 3 or 4 cells with fibres.

Downloaded from Brill.com09/25/2021 12:26:30AM via free access Rao, Rajput & Srinivas - Cambium of Sterculia 315

500

450

400

~ ..c 350 tin c <1) ....J

300

250

o A B C D E ~ Sieve tube members o Fusiform cambial cell o Vessel member

Fig. 4. Histogram showing mean length (J.un) of sieve tube elements, fusiform cambial cells and vessel members in Sterculia colorata (A), S. alata (B), S. villosa (C), S. urens (D) and S.foetida (E).

In non-conducting phloem, the sieve tubes along with companion cells become nar• row and underwent obliteration. As a result the non-conducting phloem was composed of only parenchyma and fibres. However, the parenchyma cells were larger compared to those in the functional phloem. The sieve tube members had slightly inclined end walls with simple sieve plates. Lateral sieve area occurred on both radial and tangen• tial walls. Variable amounts of callose were found on sieve areas of mature elements. Compared with fusiform cambial cells the average length of sieve tube members was slightly less while the width increased (Fig. 4). The length of sieve tube members was found to be highest in S. foetida, i. e. 449 JlIll while shortest in S. urens, i. e. 291 JlIll among all the species studied (Fig. 4). Width of the sieve tube members varied from 25 JlIll to 37 JlIll in different species. However, maximum width was found in S. villo• sa, i.e. 37 JlIll and minimum width in S. alata, i.e. 25 JlIll. Xylem in all the five species was found to be diffuse-porous with indistinct growth rings. However, the amount of wood produced during one growth period could be

Downloaded from Brill.com09/25/2021 12:26:30AM via free access 316 IAWA Journal, Vol. 17 (3),1996 determined by vascular ray noding and the presence of narrow lumen cells with thick walls in the latewood. Noding of vascular rays generally occurred in the region of the resting cambial zone. The size of the nodes varied in individual plants. In transverse section the nodes generally appeared spindle-shaped. The nodes may persist distinctly in the wood. However, the noding is not so distinct in some trees (Amobi1973). The wood fibres were nonseptate and possessed narrow lumen. Fibres were 5-8 times longer than the fusiform cambial cells. Vessel element length was heighest (450 f..Ull) in S.foetida and lowest (285 f..Ull) in S. urens. In all the five species, vessels were diffuse, solitary and in radial to tangential multiples of 2 or 3, round to oval with radial diam• eter ranging from 92-300 f..Ull. In comparison to fusiform cambial cells, the length of vessel elements had decreased (Fig. 2) but the width increased 6-12 times. Perforation plates were simple in transverse to slightly oblique end walls. Intervessel pits were alternate, round to oval and 6-8 f..Ull in diameter. Axial parenchyma were vasicentric to aliform often forming distinct tangential con• fluent bands in S. colorata, S. alata and S. urens. While in S. villosa they were scanty paratracheal and diffuse apotracheal in S. foetida. Some of the xylem ray cells were filled with phenolic deposits in S. villosa and S. foetida. However, such deposition was not noticed in the other three species.

DISCUSSION

The vascular cambium in all of the species was storied. Radial longitudinal and antic1i• nal division in fusiform cambial cells help to maintain this stratified arrangement in the adult stem. Cambial rays were compound with 2 or 3 layers of sheath cells. The occurrence of sheath cells tends to be constant in many genera of Sterculiaceae (Metcalfe & Chalk 1983). The distribution of fusiform and ray cambial cells in cambium is not consistent in the species studied. Kozlowski (1971) generalized that fusiform cambial cells occupy 90% of the total tangential area of cambial zone. However, studies on some Indian species of Dalbergia (Ghouse & Yunus 1974a) indicate thatthey occupy only up to 60% of the total tangential area of the cambial zone and their amount may fall as low as 25% in certain cases like Dillenia indica (Ghouse & Yunus 1974b). In the present study fusiform cambial cells in cambia of different Sterculia species did not exceed 75%. In all the five species of Sterculia, sieve tube members were slightly shorter than the fusiform cambial cells. Zahur (1959) and Den Outer (1986) also reported the presence of shorter sieve tube elements. However, a slight decrease in length of sieve tube mem• bers may be due to the shifting of the pointed hexagonal tip of the fusiform cambial derivatives to transverse position in sieve elements (Anand et al. 1978). Our study showed two wood anatomical groups in Sterculia species: (i) axial paren• chyma aliform to confluent in S. colo rata, S. alata and S. urens, vessel members short (length mainly less than 400 f..Ull) and no deposition of phenolics in ray parenchyma and (ii) axial parenchyma scanty paratracheal in S. villosa and diffuse apotracheal in S. foetida, vessel member longer (length mainly more than 400 f..Ull) and deposition of phenolics in ray parenchyma.

Downloaded from Brill.com09/25/2021 12:26:30AM via free access Rao, Rajput & Srinivas - Cambium of Sterculia 317

As compared with fusiform cambial cells, in all the five species of Sterculia, the width of vessel members increase 6-12 times and their length decreases slightly. The decrease in length may be due to the shifting of the pointed hexagonal tips to trans• verse position during the course of differentiation from fusiform cambial cell deriva• tives and also the radial expansion of developing vessel members. Anand et al. (1978) reported a slight decrease in length of sieve tube elements due to shifting of pointed hexagonal tips of fusiform cambial cells to transverse position. Wood fibres exhibited a maximum increase in their length, i.e. 5-8 times the length of their precursors among all the species. This can only be attributed to the intrusive growth in these elements. This feature has also been reported in many other dicoty• ledonous taxa (e.g. Bailey 1920; Chattaway 1936).

REFERENCES

Amobi, C.C. 1973. Periodicity of wood formation in some trees of lowland rain forest in Ni• geria. Ann. Bot. 57: 211-218. Anand, S.K., V.S. Sajwan & G.S. Paliwal. 1978. Size correlation among the cambium and its derivatives in Dalbergia sissoo. J. Indian Bot. Soc. 57: 16-24. Bailey,I.W. 1920. The cambium and its derivatives tissues II. Size variation and cambial ini• tials in gymnosperms and angiosperms. Amer. J. Bot. 7: 355-367. Bailey,I.W. 1923. The cambium and its derivatives tissues IV. The increase in girth of cambium. Amer. J. Bot. 10: 499-509. Berlyn, G.P. & J.P. Miksche. 1976. Botanical microtechnique and cytochemistry. Iowa State Univ. Press, Ames, Iowa. Chattaway, M. M. 1936. The relation between fibre and cambial initials length in dicotyledonous wood. Trop. Woods 46: 16-20. Cheadle, V. I., E.M. Gifford & K. Esau. 1953. A staining combination for phloem and contigu• ous tissues. Stain Technol. 28: 49-53. Den Outer, R.W. 1986. Storied structure of secondary phloem. IAWA Bull. n.s. 7: 47-51. Furqan, M. & Z. Ahmad. 1981. Ratio of ray and fusiform initials in the tree axis of Sterculia urens Roxb. at various height levels. Indian J. For. 4: 293-295. Ghouse,A.K.M. & S. Hashmi. 1977. Ray and fusiform initials in the vascular cambium of some Indian tropical trees. Geobiose 4: 149-150. Ghouse, A.K.M. & M. Iqbal. 1975. A comparative study on the cambial structure of some arid zone species of Acacia and Prosopis. Bot. Notiser 128: 327-331. Ghouse, A.K.M. & M. Yunus. 1974a. Cambial structure in Dalbergia. Phytomorphology 24: 152-158. Ghouse, A.K.M. & M. Yunus. 1974b. The ratio of ray and fusiform initials in some woody species ofthe Ranelian Complex. Bull. Torrey Bot. Club 101: 363-366. Ghouse, A.K.M., M. Yunus, F. Farooqui & D. Sabir. 1973. Occurrence of stratified cambium in some Indian tropical plants. Bangladesh J. Bot. 2: 83-87. Ghouse, A.K.M., M. Yunus & M. Iqbal. 1976. A comparative study on the cambial structure of some Bauhinia species. Bot. Jahrb. Syst. 95: 411-417. Iqbal, M. & A.K.M. Ghouse. 1983. Analytical study on cell size variation in some arid zone trees of India: Acacia nilotica and Prosopis spicigera. IAWA Bull. n.s. 4: 46-52. Khan, M. A. & A. Z. Kalimullah. 1991. Ontogenetic changes in size and amount of phloem fibres in the bark of Sterculia urens Roxb. Geobiose 18: 240-242.

Downloaded from Brill.com09/25/2021 12:26:30AM via free access 318 IAWA Journal, VoL 17 (3),1996

Kozlowski, T. T. 1971. Growth and development of trees. Academic Press, New York, London. Metcalfe, C.R & L. Chalk. 1983. Anatomy of dicotyledons. Vol. II. Clarendon Press, Oxford. Paliwal, G.S. & N.V.S.R.K Prasad. 1970. Seasonal activity of cambium in some tropical trees l. Dalbergia sissoo. Phytomorphology 20: 333-339. Rao, KS. & Y.S. Dave. 1981. Seasonal variations in the cambial anatomy of Tectona grandis (Verbenaceae). Nord. J. Bot. 1: 535-545. Rao, K S. & Y.S. Dave. 1982. Cambial activity in Mangifera indica L. Acta Bot. Acad. Sci. Hung. 28: 73-79. Rao, KS. & Y.S. Dave. 1984. Seasonal variations in the vascular cambium of Holoptelea integrifolia (Ulmaceae). Beitr. BioI. Pflanzen 59: 321-331. Silva, E.A.M., L.A.R Pereira, A.L. Pinheiro & RS. Ramalho. 1990. Seasonal variations in the cambial activity of three forest species growing at Viscosa, Minas, Gerais. Seiva 50: 49- 52. Yunus, M., D. Yunus & M. Iqbal. 1978. On the cambial structure of some industrially important tropical trees. Flora 167: 159-169. Zahur, M. S. 1959. Comparative study of secondary phloem of 423 species of woody dicotyledons belonging to 85 families. Cornell Univ. Agr. Exp. St.Mem. 358: 1-160.

Downloaded from Brill.com09/25/2021 12:26:30AM via free access