160 THE JOUKNAL OF INDIAN BOTANY
the clustered crystals in the "aqueous tissue, there is a continuous layer of rounded thin-walled cells, most of which contain clustered crystals ; it is situated beneath the sub-epidermal aqueous tissue in H. salicornicum. It may be termed a crystal layer.
General Review. — Epidermal cells have outer walls thin and more or less papillose. Stomata are depressed and guard-cells are situated in the plane of surrounding cells. The assimilatory tissue in the leaf and axis consists of palisade cells. The leaf and axis are characterised by the extensive development of an aqueous tissue, either peripheral, or central or both. The vascular system in the leaf consists of peripheral and central veins ; and it is brought into contact with the assimilatory tissue by means of sheath-cells. Hairy covering, when present, consists of uniseriate trichomes densely covered with solid papillae. Oxalate of lime occurs in the form of clustered crystals in the leaf and axis.
Sclerenchymatous pericycle is found in all the members. The vascular system in the axis consists of bundles traversing the aqueous tissue as found in species of Haloxylon and of a central cylinder as found in all the members. Bundles in the central cylinder are embedded in interfascicular wood prosenchyma in a concentric fashion. Vessels are small and have simple perforations. Medullary rays are not found in any of the members.
POLYGONACEAE.
Calligonum polygonoides L— Figs. 291, 292, Woody. Mesophyll isobilateral with a middle layer of cells with tanniniferous contents. Palisade-like cells with tanniniferous contents in the palisade tissue. Clothing hairs in the form of uniseriate trichomes. External glands club-shaped. Epidermal cells of the axis with outer walls very greatly thickened. Subepidermal groups of sclerenchyma present. Clustered crystals in the primary cortex. Pericycle of small groups of stone-cells. Wood composite. Interfascicular wood prosenchyma extensive. Meduallary rays 1-2 seriate and numerous. Pith of thick- walled cells.
Polygonum plebejum Br.— Wig. 293. Woody. Large water- storing cells intercalated amongst epidermal cells. Mesophyll of pali- sade tissue on the upper side and of arm-palisade tissue on the lower. Clustered crystal in the mesophyll. Bundle-sheath cells with tannini- ferous contents.
Epidermal cells of the axis with outer walls granulated. Collen- chyma groups subspidermal. Wood composed of xylem bundles. Pith of thin-walled cells.
