Page:The Journal of Indian Botany.djvu/138

 pith. Solitary crystals are sometimes found in groups of 3-4 in the cells ; they are sometimes also aggregated in the form of conglomerate crystals in the axis of species of Grcwia.

The veins are embedded and are not provided with bundle- sheaths in species of Gor chorus. The veins are vertically transcurrent above and below by sclerenchyma in Grcwia poimlifolia and Grcwia abutilifolia and above by sclerenchyma and below by sheath cells in Grewia villosa. The veins in species of Grcwia are provided with bundle-sheaths. In Grcwia abutilifolia there are structures of the nature of water-storing tracheids at the terminations of the veins.

Hairy covering on the leaf and axis consists of clothing and glandular hairs. The clothing hairs in species of Corchorus are unicellular, thick- walled and not dense (fig. 6G). In Grcwia they are tufted (figs. 63, 64), the constituent rays being unicellular and thick- walled. Besides the tufted hairs, there are unicellular thick-walled hairs, resembling the rays of the tufted hairs, on the axis of Grewia abutilifolia (fig. 63). The glandular hairs are club-shaped and are composed of a stalk-cell and of a head divided only by horizontal wall3 (figs. 65, 63), or by both horizontal and vertical walls (tig. 64).

Structure of the Axis : — The epidermis in species of Corchorus consists of horizontally tabular ceils with outer walls thickened and arched convexly outwards, the thickening: of the outer walls being quite considerable in Corchorus trilocularis and Corchorus tridens. The lateral and inner walls are also thickened. The epidermal cells in species of Grcwia are horizontally tabular and are uniformly thickened on all sides. The lateral walls are straight in members of both the genera.

The cortex is characterised by subepidermal cork in species of Grcwia, the innermost layers of which in G. villosa are composed of thickened and lignified cork-cells. Cork does not occur in species of Corchorus. Three tissues may be distinguished in the cortex : in species of Corchorus outermost parenchyma, middle collenchyma and innermost parenchyma ; in species of Grewia outermost cork, middle collenchyma and innermost parenchyma.

Internal secretory organs are represented in the axis of members of both the genera by mucilage cavities in the cortical parenchyma (figs. 67, 64) and in the pith (fig. 64).

The pericycle is composed of closely placed groups of stone-cells with very small lumina (figs. 64, 67). The wood forms a composite hollow cylinder. The vessels are arranged in rows. The interfascicular wood prosenchyma is extensive and is composed of cells with wide lumina. The medullary rays are numerous ; they are uniseriate in Q. trilocularis, G. vopulifolia and G. villosa, 1-2 seriate in C.