Page:The Journal of Indian Botany.djvu/688

222 THE JOURNAL OF INDIAN BOTANY in a single ring of stone-cells. In S. maritimus veins as well as the vascular bundles in the axis are enclosed in an outer ring of large colourless polygonal cells and in an inner ring of stereome.

The mesophyll in 0. rotundus and in S. maritimus is character- ised by a system of lysigenously formed cavities resulting from a deficient supply of water. Internal secretory cells with tanniniferous contents are numerous near the veins in the leaf and in the neighbourhood of vascular bundles in the axis. The mechanical tissue in the leaf as well as in the axis is mostly composed of isolated sub-epidermal girders except in 'the leaves of S. maritimus in which I-girders are found. Vascular bundles in the axis are numerous and peripheral, larger bundles alternating with the smaller.

The ground tissue is composed of thin-walled parenchymatous cells with a differentiated central tissue of much larger cells in G. rotundus. The ground tissue in S. quinquefarius is characterised by large air spaces. S. quinquefarius occurs always on wet ground and well developed aerenchyma is consequently quite necessary.

The axes of S. maritamus are enclosed in close fitting leaf-sheaths which protect the axes against insolation and also give, to some extent, rigidity to the axes against the violence of the desert winds. Leaf-blades which are as long as the axis are held in position by means of leaf-sheaths and cannot therefore be easily separated from the axis by the strong desert winds. The long leaf-blades, but for the leaf-sheaths, would have been torn off from their bases by the desert winds.

Hairs either clothing or glandular are not found on the leaf and axis.

Digitaria sanguinalis Scop. var. ciliaris Pram.— Grooved on the lower surface. Hairs spiny on the leaf and absent on the axis. Stomata more numerous on the lower surface. Articulation tissue not extensive and found on the upper side above the grooves. Palisade cells forming complet9 girders. Veins embedded and enclosed in complete sheaths. Mechanical tissue in the leaf in the form of I- girders. Webs formed by unmixed vascular bundles. Mechanical tissue in the axis forming isolated sub-epidermal girders and an internal stereome tube. Assimilatory tissue absent in the axis. Smaller bundles embedded in the stereome tube. Large bundles few in the medullary tissue. Medullary tissue of thin-walled cells.

Panicum turgidum Forsh, — Eigs..319, 320, 321. Equally deeply grooved on both sides. Margins blunt and with large stereome bundles. Hairs spiny and absent on the axis. Stomata more