Page:The Journal of Indian Botany.djvu/425

 The epidermal cells of the inid-rib are much smaller than those on the other portions of the leaf-blade. The stomata are usually equally distributed on both the surfaces. Guard-cells are elevated in Pegol- ettia senegalensis (fig. 167), Pulicaria angusti folia, E. echinatus and V. divaricata, so that the front cavity is on a level with the surface- The guard-cells are situated in the plane of the surrounding cells in other members, so that the front cavity is placed in a depression formed by the outer thickened epidermal walls (figs. 174, 184, 190). In Pegolettia senegalensis elevated stomata occur side by with depress- ed ones (fig. 167).

The mesophyll in D. tomentosa and E. echinatus, is composed of palisade tissue on the adaxiai side and of arm-palisade tissue on the abaxial side ; it is isobilateral in V. cinerascens, P. rajputanae and V. divaricata. In other members it consists of arm-palisade cells with horizontally elongated cells in the middle.

The veins are embedded except those of the mid-rib which are vertically transcurrent above and below by collenchyma. In V. cinera- scens there are a few stone-cells on the upper side of the veins. The veins of the mid-rib are quite prominent beneath and are strengthened on the lower side by arcs of stone-cells.

Internal secretory organ3 are not found except in P. rajputanae in which secretory cavities occur one on either side of the veins of the mid-rib, with a lining layer of cells and with yellowish contents. Oxalate of lime occurs in P. senegalensis, in the form of bundle of acicular crystals near the veins, in cortex and in pith.

Hairy covering on the leaf and axis consists of clothing and glandular hairs. Clothing hairs, termed " flagellum-hairs " consist of a uniseriate stalk and of a flagellum-like terminal cell in P. angusti- folia, P. rajputanae, E. echinatus and D. tomentosa ; in E. echinatus the long terminal cell is bent on the stalk as on a hinge. In V. cinera- scens (fig. 164) there are two-armed hairs, consisting of a uniseriate stalk and of a terminal unicellular two-armed cell ; the arms are unequal. The glandular hairs are of various shape. They are placed in epidermal depressions and consist of a short uniseriate stalk and of a large biseriate head in P. senegalensis (fig. 167), P. angustifolia, (fig. 172) and E. erecta. The external glands, in E. echinatus (fig. 181) and V. divaricata, consist of a long uniseriate stalk and of a head irregularly divided ; besides these there are in E. echinatus (fig, 179) spherical glands which are uniseriate, depressed and with thickened and verrucose walls. They are club-shaped in P. rajputanae (fig. 176) and are long-stalked, uniseriate and with the terminal cell much dilated to form the head in V. cinerascens (fig. 165, 166). Uniseriate, spherial and depressed glandular hairs are found in V. cinerascens