thickened and convexly arched outwards. There are large unicellular conical hair-like structures, with walls covered with cuticular knobs, intercalated amongst ordinary epidermal cells (fig. 246). The lateral walls are thin and undulated. The inner walls are thin. The cuticle is striated. The stomata are equally numerous on both the surfaces and are surrounded by ordinary epidermal cells. The guard-cells are elevated and the front cavity is on a level with the surface.
The mesophyll is bifacial. Internal secretory organs and oxalate of lime are not found. The veins are embedded and are not enclosed in bundle-sheaths. The hairy covering on the axis consists of thin- walled uniseriate trichomes. Trichomes in S. sphaerocarpa are covered with cuticular knobs. Large conical epidermal cells with walls covered with cuticular knobs (figs. 246, 247) may be of the nature of unicellular hairs in S. sphaerocarpa- The trichomes in A. linearis are smooth-walled and straight. Glandular hairs are not found.
Structure of the Axis. — Epidermis consists of tabular cells with outer walls greatly thickened and convexly arched outwards. Cuticle is striated. There are large concical unicellular hair-like structures with walls covered with cuticular knobs intercalated amongst ordinary epidermal cells in S. sphaerocarpa (fig. 247). Lateral walls are thin and straight. The stomata are like those on the leaf. The cortical parenchyma is composed of horizontally elongated cells. The cells of the outermost layer of the cortex show collenchymatous differentiation at angles in contact with the epidermal cells.
The pericycle consists of a few isolated bast fibres and of a loose ring of groups of bast fibres in S. sphaerocarpa (fig. 247) and A. linea- ris (fig. 245J respectively. The wood forms a composite hollow cylinder. The vessels in S. sphaerocarpa (fig. 247) are arranged in com- plete rows ; interfascicular wood prosenchyma is little developed and is composed of cells with thin walls and with large lumen. The vessels in A. linearis are small and are arranged in long incomplete rows ; the interfascicular wood prosenchyma is extensive and is composed of cells with thick walls and with small lumen. The medullary rays are uniseriate and numerous in A. linearis; they are absent in S. sphaerocarpa. The pith is composed of thin-walled cells.
ACANTHACEAE.
Blepharis sindica T. Anders.— Figs. 248, 249, 250. Outer walls of epidermal cells greatly thickened. Guard-cells elevated. Front cavity on a level with the surface. Mesophyll formed of palisade tissue on the upper side and of subepidermal aqueous tissue and palisade tissue on the lower. Veins provided with bundle-sheaths.
