Page:The Journal of Indian Botany.djvu/532

100 THE JOURNAL OF INDIAN BOTANY. lime absent. Veins without bundle-sheaths. Clothing hairs uniseriate trichomes. Glandular hairs spherical. Epidermal cells of the axis with outer and inner walls thickened. T. S. of the axis quadrangular. Collenchyma in the angles. Pericycle of stone-cells groups. Assimilatory tissue in the axis of palisade cells. Endodermis differentiated and with radial walls suberised. Wood composite. Interfascicular wood prosenchyma extensive and composed of cells with thick walls and with small lumen. Medullary rays uniseriate. Pith of thin-walled cells.

Structure of the Leaf.—The epidermis consists of tabular cells with the outer walls very greatly thickened. The cells on the upper side are larger than those on the lower. The lateral walls are thin and straight.

The stomata occur on both the surfaces and are accompanied by subsidiary cells. The guard-cells are elevated and the front cavity is placed in a depression formed by outer thickened epidermal walls. The mesophyll is composed of palisade tissue on the upper side and of arm-palisade tissue on the lower. Internal glands and oxalate of lime do not occur in the leaf or axis. The veins are not enclosed in bundle-sheaths. The leaves are many-ribbed. The veins of the ribs are vertically transcurrent above and below by colourless parenchyma.

The hairy covering on the leaf and axis consists of clothing and glandular hairs. Clothing hairs are in the form of uniseriate trichomes with verrucose walls (fig. 266). They are more numerous on the lower surface. The trichomes on the axis are much longer; but are otherwise like those on the leaf (fig. 267). External glands occur in two forms on the leaf and axis. They either consist of a short uni-seriate stalk and of a spherical unicellular head, or are formed of a stalk-cell an3 of a bladder-like head the cuticle of which is raised like a bladder, owing to the accumulation of secretion.

Structure of the Axis.—The T. S of the axis is quadrangular in outline with shallow grooves between the angles. The epidermis consists of small tabular cells with the outer and inner walls thickened. The outer walls are convexly arched outwards. The internal walls are thin and straight. The cuticle is thick. The cortex (fig. 267) is characterised by subepidermal strands of collenchyma situated in the angles. The assimilatory tissue consists of strands of palisade cells between the collenchyma at the angles. The endodermis is distinct and consists of thin-walled cells with radial walls suberised.

The pericycle is composed of groups of stone-cells at the angles (fig. 267). The wood is composed of large xylem bundles at the angles and of small ones between fchem. The interfascicular wood