Page:The Journal of Indian Botany.djvu/528

96 THE JOURNAL OF INDIAN BOTANY. senchyma. Wood parenchyma developed on the inner side of the xylem bundles. Medullary rays absent. Pith of thin-walled cells.

Structure of the Leaf. — The epidermis consists of polygonal cells in B. patula, B. hochstetteri and J. simplex or of tabular cells as in B. sindica. The outer walls are thickened, thickening being considerable in B. sindica. Tne outer walls are convexly arched outwards and the lateral walls thin and undulated in J. simplex. The cells are uniformly thickened on all sides in B. patula and B. hochstetteri ; the lateral walls are undulated. The lateral and inner walls are also thickened in B. sindica and the latter are undulated.

Numerous large rounded cells are intercalated amongst ordinary epidermal cells ; and each contains a spherical cystolith (fig. 258), The stomata are accompanied by subsidiary cells. The guard-cells are usually elevated and the front cavity is on a level with the surface in all members except B. hochstetteri in which the guard-cells are in the plane of surrounding cells and the front cavity is a little depressed. The stomata are more numerous on the lower surface except in B. sindica where they are more numerous on the upper surface. This may be accounted for by the occurrence of subepidermal aqueous tissue on the lower side where there should be as few stomata as possible to economise the supply of water contained in the aqueous tissue. The mesophyll is isobilateral except in B. patula in which it consists of palisade tissue on the adaxial side and of arm-palisade tissue on the abaxial side. In B. sindica there is palisade tissue on the adaxial side and subepidermal aqueous tissue and palisade tissue on the abaxial side.

In B- hochstetteri and J. simplex there are peculiar structures on both sides of the mesophyll. They are at some places circular in section and are composed of irregular cells faintly green in colour ; at other places they have the form of secretory cavities with bounding cells projecting into them (fig. 258). These structures probably represent the internal secretory organs. Oxalate of lime does not occur in the form of crystal sand in the cell-cavity of clothing hair8 on the leaf and in the epidermal cells of the axis of B. sindica. The veins are embedded and are not enclosed in bundle-sheaths.

The hairy covering on the leaf and axis consists of clothing and glandular hairs. The clothing hairs in B. patula (fig. 251) and J. simplex (fig. 258) are simple uniseriate trichomes with thickened and muriculate walls ; the constituent cells in the former are dilated at the lower end and give a jointed appearance to the trichomes. In B. hochstetteri there are unicellular elliptical hair-like structures with walls thickened and muriculate on the leaf ; on the axis, besides the long simple uniseriate trichomes (fig. 255), there are other special