Page:The Journal of Indian Botany.djvu/684

2L8 THE JOUKNAL OF INDIAN BOTANY. pact structure. Lateral walls are thin and straight. The upper epidermis forms the aqueous articulation tissue and is many-layered in species of Cyperus. The articulation tissue in the mid-rib of G. rotundas (fig. 303) and S. mar Minus consists of elongated cells narrowed above so as to form a specialised articulation tissue to regulate the upward curving movements of the leaf-halves by the difference in the turgidity of these cells. As these cells are greatly narrowed in their upper portion, the leaf-halves can come quite close together and thus protect the articulation tissue from suffering much loss of water in times of very dry weather. Such a tissue in the mid-rib is not necessary in other species of Cyperus, as there is abundant aqueous tissue and as the leaf-halves are very short. In F. tenera the articulation is 2-3-layered in the mid-rib.

Margins are rounded in C. rotundas or are bluntly pointed as in other species of Cyperus and in S. maritimus or peculiarly angular in F. tenera (fig. 308).

Stomata in species of Cyperus and in F. tenera occur only on the lower surface of the leaf ; in S. maritimus they are more numerous on the lower surface. The occurrence of stomata only on the lower surface is due to the presence of the assimilatory tissue below the lower epidermis ; their presence on the upper surface, where the articulation tissue is developed, will accelarate transpiration and will thus perform a function opposite to that of the articulation tissue. The occurrence of stomata on both the surfaces in S. mariti- mus is partly due to the absence of aqueous tissue near the surface and partly to the presence of photosynthetic tissue along both the surfaces. The guard-cells are elevated and are accompanied by subsidiary cells in all the members. The front cavity is placed on a level with the surface in C. rotundas, while in other species of Cyperus and in S. maritimus it is placed in a depression formed by outer thickened epidermal walls ; in F. tenera it is elevated above the surface.

The stomata on the leaf as well as those on the axis of all members have on obconical sub-stomatal cavity which is lined by elongated cells forming an obconical tissue. The obconical cavities are quite conspicuous in C. conglomerates (figs. 299, 303, 302) and also occur below the epidermis even where stomate do not occur. The obconical shape of sub-stomatal cavities and also that of the sub-stomatal tissue forms a characteristic feature of members of Cyperaceae. Stomata occur on the outer surface of the leaf-sheath of S. maritimus. Stomata on the leaf-sheath as well as those on the axis like those on the leaf.

The photosynthetic tissue in species of Cyperus and in F. tenera is composed of complete girders of tubular palisade cells round all the