Pror Indian Acad. Sci., Vol. 87 B (Plant Sciences-4), No. I1, November 1978, pp. 335-346, 9 printed in India A further investigation of the morphology of vessels in Marsilea D S LOYAL and HARMOHINDER SINGH Botany Department, Panjab University, Chandigarh 160 014 MS received 3 March 1978 Abstract. Morphology of vessel members in 7 species of Marsilea is described. The roots in all species examined possess vessels with scalariform (original), scalari- form-porous and simple (specialised state) perforation plates; these variables axe re- corded in the different regions of the same root. Vesselsof distinct morphology are also recorded for the first time in the rhizome~root-petiolejuncture. Their origin and evolution in roots, and their absence in the internodal parts of the rhizome and petiole are discussed. Past comparison between Marsilea and Pteridium vessels is reviewed. Keywords. Marsilea; morphology of vessels. 1. In~oducflon Vessel members were reported for the first time by White (1961) in the roots of 3 species of Marsilea, M. quadrifolia, M. hirsuta and M. drummondi. He also recorded their absence in the rhizome and leaves of the same species. Mehra and Soni (1971) made a few sketchy observations on 4 species from the Indian subcon- tinent, namely, M. minuta, M. aff-sinensis,* M. quadrifolia and M. poonensis. More recently, Bhardwaja and Baijal (1977) have recorded vessel members purported to be occurring in the rhizome of M. drummondi and M. elata. Our present study encompassing 7 distinct species, M. minuta L. (diploid eytotype), M. minuta* (tri- ploid eytotype), M. aegyptiaca Wall., M. diffusa A. Br., M. quadrifolia L. M. drum- mondi A. Br., M. vestita Hook. et. Grey. and M. rajasthanensis Gupta, has shown that the results published by the above mentioned authors from India do not faith- fully represent all the morphological diversity of the xylem elements involved. Hence, one of the objectives of the present study was to assess the validity of the previous conclusions based upon insufficient observations. 2. Materials and methods Of the 7 species investigated, the material of M. minuta (diploid eytotype) and M. minuta (triploid eytotype) was coUected from a number of wild localities around *The commonly occurring triploid cytotype of Maralea minuta from the Indo-gangetic plains (Mehra and Loyal 1959) was identified as M. affi-sinensis Hand-Mazz. (Cf. Mehra-Alston Panjab University Herbarium Sheet Nos. 84, 85). Gupta (1962) gave it a varietal rank, indica. However, pending typification of this cytotype, we denote it as M. minuta (triploid cytotype) in the present paper. 335 336 D S Loyal and Itarmohinder Singh Chandigarh and District Ambala. The material of remaining 6 species, namely, M. quadrifolia, M. drummondi, M. aegyptiaca, M. diffusa, M. vestita and M. rajas- thanensis was obtained through the courtesy of Dr T N Bhardwaja, Government College, Ajmer, Rajasthan. Plants were fixed in FAA and bits of rhizome, roots and petiole were macerated in Jeffrey's macerating fluid. After warming for about 5 rain over the spirit flame the material was left in the macerating fluid for nearly 2 hr after which the xylary elements were isolated and finally mounted in appropriate concentration of glycerol. 3. Observations 3.1. Morphology of vessel members in roots All the elements examined were exclusively those which comprised the metaxylem. However, owing to the mesarch condition of xylem it was difficult to ascertain the position of a given element in the early or late part of the metaxylem. In agree- ment with the earlier authors, vessel members are present in roots of all the species investigated. As depicted in figures 1-8, 21-25, 28, 31-34, the vessel members differ in: (a) length/diameter, (b) nature of perforation, (c) angle of inclination of the end wall i.e. long or short slants, transverse and (d) pitting pattern of the overlap and lateral wall area. Figures 3 and 4 illustrate elements with smallest diameter and those illustrated in figures 8, 33 and 34 are the largest in our sample; the remaining elements, as depicted in figures 1, 2, 5--7 may be regarded as intermediate in size. A compari- son of figures 1-8, 9 with figures 20 and 21 reveals that the angle of inclination of the end walls of the elements not only differs from element to element in the same organ but also of the two ends of the same element. Generally, the transverse or truncate end walls are observed in the vessels of relatively large diameter. As regards the nature of perforation, the elements exhibit both the original scalari- form perforation (figures 20, 21) as well as specialised state i.e. simple perforation (figures 1-3, 5, 8); the latter condition is however observable in overwhelmingly large number of elements in all the species investigated. The scalariform perforate plates may be present on long (figures 20, 21) or short slants and the number of intervening bars may vary, e.g. from 6 (figure 31) to as many as 20-26 (figures 20, 21). The elements with reduced width of intervening bars on long slants are sugges- tive of their being nearest to the ' presumptive vessels' recorded earlier in two ter- restrial ferns, Woodsia ilvensis and Notholaena sinuata (White 1963b). Also, in certain scalariform perforate elements, for instance, as shown in figure 20, it was difficult to ascertain whether or not a few pores/pits situated on the lower as well as upper ends of the perforation plate are pores in the strict sense of the term, i.e. characterised by the absence of pit-closing membranes. In order to study the variation pattern of perforations in individual vessels through- out the length of a given root, we analysed the roots of 3 species, M. quadrifolia, M. drummondi and M. minuta (triploid cytotype). As schematically shown in figure 9, in the case of M. quadrifolia, the vessel members in the middle portion of the root are simple perforate with transverse end walls. Progressively toward the distal as well as the proximal part of the root, the elements are characterised by Morphology of vessels in Marsilea 337 Figures 1-9. Selected vessel members in the roots (• 875). 1, 2. M. minuta triploid cytotype. 3. M. aegyptiaca. 4. M. vestita. 5, 6. M. rajastltane~is. 7, M. quadri- folia. 8. M. drummondi. 9. Diagrammatic representation depicting the root-rhizome course of vessel members in M. quadrifolia. Note the variation in angle of inclination of the end wall and the perforation plates in different portions of the root. 338 Er~S Loyal and Harmohinder Singh Figures 10-15. Selectedvessel members in the root-rhizome-petiole juncture (x 875). 10-12. M. minuta (triploid cytotype). 13. M. aegyptiaca. 14-15. M. rajasthanensis. Morphology of vessels in Marsilea 339 Figures 16-19. Selected vessel members in the root-rhizome-petiole juncture (x 875). 16. M. rayasthanensis. Note the presence of perforation (arrow) on one end of a branched vessel member, the other end is imperforate. 17. M. diffusa. 18. M. drum- mondi. 19. M. quadrifolia. Morphology of vessels in Marsilea 341 Figures 20-.38. (Seecaption~ in page 346) 342 D S Loyal and Harmohinder Singh soalariform or sealariform-porous perforations on long or short slants. As expected, the vessel members which are located in the root.shoot-petiole juncture, and are co- oriented with those of the root below, have perforation on one end only, the other end being invariably imperforate (figures 9, 16). In M. minuta (triploid cytotype) and M. drummondi, on the other hand, the elements tend to have simple perforations for most part of a given root. Pending further developmental study, it seems possi- ble that the nature of perforation is determined by the hitherto unknown morpho- genetic factors which operate differentially at different stages of the root ontogeny. Further study is obviously necessary to elucidate this aspect of vessel differentiation in relation to their geography. 3.2. Vessel members in root-rhizome-petiole juncture As pointed out earlier, White (1961) did not observe any vessel members in the rhi- zome and leaves of the species he investigated. During the course of our studies on water ferns in general (Loyal 1973) and while tracing the course of individual vessels in a given root, the last vessel members in the root were located in the nodal part of the shoot (figure 9). The vessel members in the above-mentioned region of the rhizome of M. minuta (triploid eytotype), M. aegyptiaea, M. diffusa, 3/I. rajasthanensis, M. quadrifolia and M. drummondi, are charaeterised by scalariform--porous perforations on bulbiform (figures 12, 19), curved, spatulate ends (figures 11-17, 19); simple-perforate elements on swollen ends are present in a tiny proportion only (figures 11-13). As depicted in figures 14, 15, 18, 19, simple perforations arise as a consequence of breakdown of bars. The perforation may be present on short (figures 11, 13) or on long slants (figure 27). It is clear from the foregoing that the simple perforate elements on truncate end walls such as those claimed to have been seen by Bhardwaja and Baijal (1977) are absent in our species which incidently include those worked out by the above authors. Stated succinctly, the perforate elements herein portrayed by us, serve as markers for the rhizome-root-petiole juncture and, therefore, a re-examination of Bharadwaja and Baijal's preparations will be necessary. 3.3. Pitting patterns of overlap and lateral wall area In all the three organs, viz., rhizome, root and petiole we have observed 6 types of pitting patterns: (a) scalariform, Co) trans-edge opposite, uniseriate (figures 31, 32), (c) trans-edge opposite (figures 33, 34), (d) trans-edge alternate, (e) irregular or mixed (figures 35, 36) and (f) obscalariform (figure 38).