Page:The Journal of Indian Botany.djvu/686

220 THE JOURNAL OE INDIAN BOTANY. angular margin and is supported by angular sfcereome bundles ; other veins are small and are placed in the middle of the mesophyll.

In the leaf-blade and leaf-sheath of S. maritimus veins are enclosed in an outer ring of stereome and in an inner ring of large colourless polygonal cells. All the veins are vertically transcurrent ; those in the leaf -blade are vertically transcurrent above and below by aqueous cells and those in the leaf-sheath are apposed to lower epidermis and are vertically transcurrent above by aqueous cells.

The mechanical tissue in G. rotundas (figs. 303, 304) and in C. nivens (fig. 298) is composed of isolated sub-epidermal girders, which are more numerous on the lower surface. On the lower surface the subepidermal girders are found above the veins and on the upper surface they occur at regular intervals, being developed more or less above every alternate vein in (J. rotundas. In G. niveus there are some I-girders in association with the larger veins, webs of which are formed by unmixed vascular bundles. In C. conglomcratus and in G. arenarius isolated sub-epidermal girders occur only on the lower surface above the lower veins; and there is a long sub epidermal girder on the upper surface near one margin (fig. 300). The mechanical tissue in F. tenera is represented by sub- epidermal girders in the angular margins and below the mid-rib which is greatly projected downwards. The mechanical tissue in leaf-blades of S. maritimus (fig. 312) consists of I-sub-epidermal girders webs of which are formed by mixed vascular bundles of the veins and of small sub- epidermal girders in the margin and on the lower surface of the mid-rib. The sub-epidermal girders in leaf-sheaths occur on the outer surface above the veins and at the angles.

The occurrence of extensive mechanical tissue on the lower surface protects the lower surface against tension produced in the upwards-curving movement of the leaf-halves which are brought about by diminution in turgidity of the cells in the articulation tissue in the upper half of the leaf-blade.

Hairs, either clothing or glandular, are absent in all the members.

Structure of the axis. — The epidermis consists of tabular cells with outer walls flat, greatly thickened and silicified. Inner walls are very thin and angular and lateral walls are thin and straight. Epidermal cells between the girders in species of Scirpus are uniformly sclerosed.

The assimilatory tissue in species of Cyperus and in F. tenera is composed of girders and arcs of tabular palisade cells round smaller veins and on sides of the upper portion of larger veins respectively. In S. quinquefarius (figs. 309, 310) palisade tissue occurs between and below the girders, while in 8. maritimus (fig. 315) it occurs between the girders.