Page:The Journal of Indian Botany.djvu/535

PLANTS OF THE INDIAN DESERT. 103

Aerua tomentosa Forsk.— Figs.:271, 272, 273, 274. Mesophyll bifacial. Veins with bundle-sheaths. Mid-rib prominent above and below. Clustered crystals in the leaf and axis. A dense covering of candelabra hairs on the leaf and axis. Collenchyma in the angles of the axis. Assimilatory tissue in the axis chloreuchymatous. Pericycle of groups of stone-cells. Pith of thick-walled cells.

Aerua pseudo-tomentosa Blatt. & Ball— Figs. 275, 277, 280, 281. Mesophyll bifacial. Clustered crystals in the leaf and axis. Veins with bundle-sheaths. Mid-rib furrowed above and prominent below. A dense covering of candelabra hairs on the leaf and axis. Assimilatory tissue in the axis formed of palisade cells. Collenchyma in the angles. Pericycle of groups of stone-cells. Pith of thick*walled cells.

Achyranthes aspera L.— Figs. 282, 283, 284. Mesophyll bifacial. Clustered crystals in the leaf and axis. Veins without bundle-sheaths. Clothing hairs in the form of uniseriate trichomes with walls knobbed. Glandular hairs with a uniseriate long stalk and with an ellipsoidal head. Collenchyma in the angles. Assimila- tory tissue in the axis chlorenchymatous. Pericycle of groups of stone-cells and isobilateral. Two vascular bundles in pith. Pith of thin-walled cells.

Pupalia lappacea Moq.— Figs. 276, 278, 279. Mesophyll bifa- cial. Oxalate of lime in the form of clustered crystals in the leaf and that of crystal sand in the axis. Veins without bundle-sheaths. Hairs uniseriate, curved and smooth-walled. Collenchyma in angles. Assimi- latory tissue in the axis chlorenchymatous. Pericycle of groups of stone-cells and isobilateral. Pith of thin- walled cells.

Structure of the Leaf. — The epidermis consists of tabular cells with the outer and inner walls thickened and convexly arched outwards and inwards respectively. The lateral walls are thin and straight. The stomata are more numerous on the lower surface and are surrounded by ordinary epidermal cells. The guard-cells of the stomata on the upper surface are in the plane of surrounding cells and the front cavity is placed in a depression formed by outer thickened epidermal walls (fig. 275). The guard-cells of the stomata on the lower surface are a little elevated and the front cavity is on a level with the surface. The stomata on the axis are placed in depressions formed by outer thickened epidermal walls. The stomata are replaced by lenticels in the rhizomatous axes of A. tomentosa.

The mesophyll is composed of palisade tissue on the upper and of spongy tissue on the lower. Oxalate of lime occurs in the form of