Page:The Journal of Indian Botany.djvu/602

162 THE JOURNAL OP INDIAN BOTANY. parenchymatous and hold tanniniferous contents in both the mem- bers.

Wood forms of a composite hollow cylinder in G. polygonoides, while in P. plebejum it consists of xylem bundles connected by strands of interfascicular wood prosenchyma. Vessels in G. polygonoides are small and few; they are uniformly distributed in extensive interfasci- cular wood prosenchyma formed of small cells with thick walls and with small lumina. Medullary rays are present only in C. polygonoi- des and are 1-2 seriate. Vessels in the xylem bundles of P. plebejum are many and large and the connecting strands of interfascicular wood prosenchyma are formed of cells with thin walls and with large lumina. Wood parenchyma is little developed.

Pith consists of thin-walled and thick-walled cells in P. plebejum and G. polygonoides respectively.

Oxalate of lime is found in the form of clustered crystals in the assimilatory tissue and in cortical parenchyma near the pericycle. Secretory cells with tanniniferous contents occur in the epidermis, cortical parenchyma and pith in species of both the genera, Tannin is also found in the medullary ray-cells of G. polygonoides.

The mechanical tissue consists of sub-epidermal strands and of pericyclic stone-cell groups. Sub-epidermal strands are collenchy- matous in P. plebejum, while those in G. polygonoides are formed of stone-cells. Sub-epidermal strands and the pericyclic stone cell groups together form a system of I-girders, the webs being formed by the assimilatory tissue. The occurrence of the mechanical tissue in the form of I-girders in the periphery of the axis forms a suitable strengthening tissue in the axis which is exposed to the strong winds of the desert.

Aristolochia bracteata Eetz. — Epidermis of tabular cells. Stomata found on both the surfaces and accompanied by ordinary cells. Mesophyll bifacial. Clothing hairs uniseriate and bracket-shaped. Veins embedded and with bundle-sheaths.

Structure of the leaf. — The epidermis consists of tabular cells with outer walls thickened and convexly arched outwards. Late- ral walls are thin and straight. Stomata are more numerous on the lower surface and are accompanied by ordinary epidermal cells. Guard- cells are in the plane of surrounding cells and the front cavity is placed in a depression formed by outer thickened epidermal walls.

Hair convering consists of a few clothing hairs which are uniseriate and bracket-shaped. They are composed of a unicellular dome-shaped pedestal seated on epidermal cells, of a neck and of a