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Vessels in some aslepiadceae.

In the present investigation vessels of 16 species of family Asclepiadaceae have been studied. Through a lot of variation exists in the size and shape of vessels, number of perforation plates and intravascular thickening of walls in the taxa, the vessels in asclepiadaceae are found highly specified.


INTRODUCTION
The xylem occupies a unique position among plants tissues in that the study of its anatomy has come to play an important role with reference to taxonomy and phylogeny. The lines of specialization of the various structural features have been better established for the xylem than any other single tissue (Bailey 1944;Bailey and tupper 1918;Chalk, 1933;Tippo 1940). Dwarfed and extremely xerophytic plants frequently have abnormally short vessel members owing to excessive reduction in size of cambial initials. It should be recognized that the vessel members fluctuate more or less in size and structure within the limits of single plant (Bailey and Tupper 1918).
A few workers have worked on the tracheary elements of certain taxa of the family Asclepiadaceae. In view of this the present investigation is undertaken.

Materials and Methods:
Sixteen species (Table-1) of the family Asclepiadaceae were collected from different part of rajasthan and fixed in F.A. A. longitudinal sections of stem were cut and then tissues were macerated following the method of Jane (1956). After through washing the macerated material was stained in Saarinen and mounted in glycerin jelly.
Camera lucida drawings were made using the same magnification to depict the variation in size, shape, location and number of perforation plates. Mean values of 10 observations were taken.

Observation:
The vessels are classified into three types viz, long, medium, short. The length and diameter of vessels µm , number and position of perforation plates and nature of adjacent wall thickening are given in (Table-1). Fig. 1 shows variations in the structure of tracheary elements in species of the family Asclepiadaceae.
Pages 168-173 D. The average length and diameter of long, medium, short sized vessels ranges from 663-84 µm and 70-15 µm respectively the maximum average length is observed in Calotropis procera and minimum in Cryptostegia grandiflora whereas the largest diameter is seen in Stcphanotis floribunda and smallest in Tylophora indica (maroon colored flower).

II. Shape of vessels -
The shape of vessels is highly variable, Tubular, Cylindrical and Conical vessels are common of occurrence. In addition to these type, drum-like vessels are found in Marsdenia tenacissima (Fig 1  T); Pergularia daemia ( Fig. 1 U); Cryptostegia grandiflora. Spindle shaped in Calotropis procera ( Fig. 1. L), Gymnema sylvestre ( Fig. 1 K) and column-like in Cosmostigma racemosum (Fig 1.V), beside this most of the vessels show no definite shape and it may be intermediate between tubular, cylindrical conical, drum-like and spindlelike.
IV. End-Walls of vessels -in all the species of this family blunt end wall of the vessel is a common feature. In addition to this, forked end wall is observed, in Hemidesmus indicus (Fir.1 R), and Tylophora indica (maroon coloured flower) (Fig. 1 H) Pointed, short or long end walls are seen in Tylophora indica (maroon coloured flower) (Fig.1 A), Hemidesmus indicus (Fig 1 F) and Pergularia daemia ( Fig. 1. O).
V. Thickening of vessel wall: All the species studied exhibit simple pits on adjacent walls. The orientation of simple pits is either alternate or scattered regularly.
The orientation of pits is mostly transverse or oblique. The simple pits are mostly spherical but rarely elongated. Reticulate pitting is observed in Telosma pallida, Oxystelma secamone and Calotropis buchanani, Asclepias curassavica and Tylophora indica (cream coloured flower) exhibit bordered pits. "Shah, Nila Shah and Bhatt (1973) reported that in Pergularia daemia the average size of short, medium and long vessels of the root respectively is 190, 285 and 480 µm in length and 39, 108 and 162 µm in diameter. In the present study these dimensions in respect of stem are 44, 160 and 240 µm for length and 20-16 µm for diameter. Prasad, Wahi and Jonaja (1961) recorded the size of the vessel of root in Marsdenia to be 225-450 µm in length and 35-150 µm in diameter.
From the above discussion it is clear that there is lot of variation in size and shape of vessels, number of perforation plates and intervascular thickening of walls in the Asclepiadaceae, Severalworkers (Shah et al. 1967, Chaedle and Kosakai, 1975, 1976Abbe and Abbe, 1971;Bailey, 1944;Inamdar and Murthy, 1977;Nag & Kshetrapal, 1988) have reported variations in vessel characters in different taxa of Angiosperms. The vessels in Asclepiadaceae are highly specialized in having simple perforation plates. Apocynaceae are also highly specialized in having simple perforation plates. Apocynaceae are also highly specialized in having simple perforation plates (Nag & Kshetrapal, 1988.