PLANTS OP THE INDIAN DESERT. 97
forms which consist of a stalk-cell and of a terminal cell which is unicellular and two-armed and sometimes with a small scale on its upper side (figs. 256, 257). The walls of these different forms of hairs in B. hochstetteri are muriculate. The clothing hairs in B. sindica (fig. 249) are unicellular and conical and have walls thickened and muriculate.
External glands occur on the leaf and axis of all members. In B. sindica, B. patula and J. simplex they are placed in epidermal depressions and consist of a stalk-cell and of a spherical head divided by horizontal and vertical walls (fig. 258). Glandular hairs on the axis of B. patula and on the leaf and axis of B. hochstetteri, consist of a long uniseriate stalk and of a disc-shaped head divided either by a vertical walls (figs. 253, 255) or both by horizontal and vortical walls. Structure of the Axis. — The epidermal cells are tabular in B. sindica and J. simplex ; they are polygonal in B. hochstetteri and B. patula. The outer walls are thickened. There are numerous large cells, circular in T. S., intercalated amongst ordinary epidermal cells, each containing a rounded cystolith (fig. 251). The stomata on the axis are like those on the leaf. The stomata situated on the sides of furrows in B. hochstetteri, however, are elevated a good deal above the epidermis.
The primary cortex is characterised by the occurrence of collenchyma which forms larger groups at the angles and smaller ones between them. The collenchyma in B. sindica forms a continuous ring. The assimilatory tissue in B. patula and B. hochstetteri is formed of chlorenchyma, while in J. simplex it consists of large thin-walled cells which occasionally act as water-reservoirs.
Sclerenchymatous pericycle is not developed except in B. sindica and B. patula, in which it consists of isolated bast fibres The wood is composite in all members; it is of uniform breadth except in B. patula, in which it is much narrowed at two opposite points. The wood in B. hochstetteri and J. simplex, is composed of large xylem bundles at the angles connected by strands of interfascicular wood prosenchyma with a few rows of vessels embedded in them. The vessels in B. sindica and B. patula are uniformly distributed in the interfascicular wood prosenchyma. The narrowed portions of the wood-ring represent the plane at right angles to the direction of the wind. The medullary rays are uniseriate. They are numerous in B. hochstetteri. The wood parenchyma is little developed in B. sindica and B. hochstetteri while in B. patula and J. simplex it occurs in groups on the inner side of the angular xyem bundles.
The pith is composed of thin-walled cells except in R. patula in which it consists of thick-walled cells. Oxalate of lime is found in
