axis. The pith is composed of thick-walled cells and is characterised by sieve-sclereids.
CELASTRACEAE.
Gymnosporia montana Benth.—'Figs. 86, 87. Upper epidermis locally two-layered. Lower epidermis formed of vertically elongated and papillose cells. Mesophyll consisting of palisade tissue on the adaxial side and of arm-palisade tissue on the abaxial side. Internal glands consisting of cells with tanniniferous contents in the loaf and axis. Oxalate of lime not occurring in any form. Veins vertically transcurrent and enclosed in bundle-sheaths. Hairy covering absent. Pericycle composed of groups of stone-cells. Cork sub- epidermal. Wood prosenchyma formed of cells with thick walls and small lumina. Medullary rays 1-2 seriate. Pith heterogenous.
Structure of the Leaf.—The upper epidermis consists of tabular cells, with inner walls convexly arched inwards ; it is locally two- layered by division walls which may be thin or thickened and which are parallel to the surface of the leaf. The lower epidermis consists of polygonal cells which are greatly elongated vertically and are drawn out into papillae (fig. 86). Outer walls are thickened; inner walls are also thickened except in some cases, when the upper epidermal cells are divided by walls parallel to the surface. The lateral walls are thin and straight. The tendency to form a two-layered epidermis as well as the palisade-like elongation of the epidermal cells are adaptations to protect the palisade tissue against insolation as well as to check transpiration by depressing the stomata.
The stomata are numerous only on the lower surface and are surrounded by ordinary epidermal cells. The guard-cells are depress- ed and the front cavity is placed in a deep depression formed by the palisade-like surrounding cells.
The mesophyll is composed of palisade tissue on the adaxial side and of arm-palisade tissue on the abaxial side. In the mesophyll there are numerous cells with tanniniferous contents. Secretory cells with tanniniferous contents are abundantly found in all tissues of the axis, Tanniniferous contents are found in cortical parenchyma, in cells separating the groups of stone-cells of the pericycle, in numerous cells in the soft bast and in the medullary ray cells which are opposed to the glandular cells between the pericyclic stone-cell groups. Oxalate of lime does not occur in any form in the leaf or axis.
The veins are enclosed in green bundle-sheaths and are vertically transcurrent above and below by colourless thick-walled parenchyma. There are small groups of stone-cells on the lower side of the phloem of larger veins, thus protecting it.
