Page:The Journal of Indian Botany.djvu/428

 The wood is composed of xylem bundles or forms a composite hollow cylinder, as will be seen from the tabular form. Vessels have simple perforations. The interfascicular wood prosenchyma is well developed only in V. cinerascens (fig. 165), P. senegalensis and P. raj- patanae (fig. 173) ; medullary rays are found only in these members. Other members are more or less herbaceous and the structure of wood does not follow any definite lines of development, as it is found to vary in the same species.

The wood parenchyma is little developed and occurs on the inner side of fehe xylem bundles. The pith consists of thin-walled cells in all members except V. cinerascens and P. rajputanae where it is formed of cells with thick and lignified walls. Some of the pith cells of P. rafpidanae contain black granular contents (fig. 173 G).

Anamolous structures are represented by small medullary xylem bundles close to the inner side of the wood cylinder of P. rajputanac (fig. 173 C).

Salvadora persica L.— Figs. 191, 192, 193. Epidermis of the leaf locally two-layered. Larger veins with arcs of stone-cells on the lower side. Vascular ring more or less dumb-bell shaped. Vessels in the narrowed portion very small. Soft bast forming a continuous ring and following the outline of the wood cylinder.

Salvadora oleoides Dene.— Figs. 194, 195, 196. Epidermis of the leaf uniformly two-layered. Vains with sclerenchyma on their upper and lower side. Short unicellular hairs found on branches. Wood forming a hollow cylinder of uniform breadth. Medullary rays continuous with cortical parenchyma. Soft bast forming groups.

Structure of the Leaf. — The epidermis in S. persica (fig. 191) is locally two-layered. The epidermal cells are tabular with outer walls thickened. The inner and lateral walls are also a little thickened and the former are convexly arched inwards. The epidermis in S. oleoides (fig, 194) is uniformly two-layered on both sides. The outer layer is formed of small tabular cells with the outer and lateral walls thicken- ed ; the inner layer consists of large thin- walled tabular cells with the inner walls convexly arched inwards, so as to come into close contact with the assimilatory tissue. There are a few large thick- walled ovoid epidermal cells found below the epidermis on both sides in either species; these cells probably have a water-storing function.

The stomata are associated with subsidiary cells and occur abund- antly on both the surfaoes. The guard-cells are situated in the plane of surrounding cells. The front cavity is usually situated in the de-