Page:The Journal of Indian Botany.djvu/784

276 THE JOURNAL OF INDIAN BOTANY. Glandular hairs are of rare occurrence. They occur on the upper surface of the leaf-blade of 0. Thomaeum, on the axis of G. Boleana (fig. 342) and on the leaf-blade and axis of D. bispinata. They are composed of a stalk-cell and of a club-shaped head which is divided by horizontal walls.

Structure of the axis. — The epidermal cells are small and have the outer walls greatly thickened and silicified. The stomata are accompanied by subsidiary cells. The guard-cells are elevated and the front cavity is placed in a depression formed by outer thickened epidermal walls.

The cortex is characterised by an extensive sclerenchymatous tissue with groups of the assimilatory tissue embedded in it. The assimilatory tissue, in A. hirtigluma, P. turgidnm, E. interruputa, E. aristata, and G. Royleana is composed of groups of palisade cells which are separated from the stereome by single layers of thick- walled cubical cells containing chlorophyll and resembling bundle- sheath cells.

The palisade cells form a continuous ring in P. elegans and E. hirsutus. An assimilatory tissue is not found in D. sanguinalis, E. Boyleanus, L. senegalensis and species of A ndropogon. In other members the assimilatory tissue is chlorenchymatous and is not accompanied by a sheath-like layer.

The mechanical tissue in the axis is represented by a stereome tube supplemented by isolated sub-epidermal girders of variable sizes except in P. elegans and E. hirsutus. Flanges are given out from the outer side of the stereome tube at more or less regular intervals and in some cases (figs. 340, 355), they unite with supplementary sub-epidermal girders, thus bringing the two systems into contact and contributing additional strength to the whole mechanical system. In species of Aristida (figs. 336, 337), Panicum (figs. 320, 322) and of Eleusine (fig3. 348, 350), in P. elegans (fig. 352), G. Boyleanus (fig. 343) and C. catharticus (fig. 324) the smaller vascular bundles are embedded in the stereome strands, formed by sub-epidermal girders and by flanges of the stereome tube.

The embedded small vascular bundles are mixed with the accom- panying sheaths (fig. 320) only, or with both sheaths and girders of the assimilatory tissue (figs. 340, 343, 352). In other cases where the vascular bundles are embedded they are unmixed. This sort of arrangement of the mechanical tissue is quite effective, as it forms an adequate strengthening tissue without preventing the assimilatory tissue from performing its function.

In D. sanguinalis, E. Boyleanus, L. senegalensis and in species