Page:The Journal of Indian Botany.djvu/233

 a short uniseriate stalk and of an ovoid curved head. Pericycle formed of a composite ring of stone-cells. Axis ribbed. Ribs strength- ened by collenchyma. Assimilatory tissue in the axis formed of chlorenchyma. Wood formed of xylem bundles connected by strands of interfascicular wood prosenchyma. Medullary rays absent. Pith formed of thin walled cells.

Structure of the Leaf : — The epidermis consists of tabular cells which are much larger on the upper surface. The outer walls are a little thickened ; the inner walls are gelatinised, and those of the upper epidermis are greatly arched convexly inwards. The lateral walls are very thin and straight. The gelatinisation of the inner walls of the epidermal cells compensates for the hairy covering which is scanty. The stomata are more numerous on the lower surface, and are surrounded by ordinary epidermal calls.

The mesophyll is composed of palisade tissue on the adaxial side and of arm-palisade tissue on the abaxial side. Internal secretory organs do not occur in the leaf. They are represented in the axis by secretory cells with tanniniferous contents in the soft bast and pith. Oxalate of lime occurs in the form of numerous clustered crystals near the veins in the leaf. The clustered crystals occur in a layer of cells outside the pericycle and in the pith of the axis.

The veins are provided with green bundle-sheaths. The leaves are many-ribbed and the veins of the ribs, which are prominent below, are vertically transcurrent above and below by collenchyma. The smaller veins are embedded.

The hairy covering consists of clothing and glandular hairs. The clothing hairs on the leaf are short, thick-walled, unicellular and with a sharp point. The clothing hairs on the axis are longer with muriculate walls; "the basal portion is divided by two to three cross- walls. The glandular hairs are formed of a short uniseriate stalk and of a small ovoid head which is curved and is divided by horizon- tal walls (fig. 95).

Structure of the Axis : — The axis is ribbed. The epidermal cells are small and vertically tabular with outer walls greatly thick- ened and convexly arched outwards. The primary cortex is formed of chlorenchyma which is bounded internally by a layer of thin- walled colourless cells mostly containing clustered crystals. Strands of collenchyma are developed in the ribs.

The pericycle is formed of a composite ring of stone-cells. The wood is composed of xylem bundles connected together by narrow strands of interfascicular wood prosenchyma formed of cells having thin walls and large lumina. The vessels are very large and have simple perforations. Medullary rays are absent.