Page:The Journal of Indian Botany.djvu/228

 both the surfaces. Guard cells elevated. Mesophyll composed of palisade tissue on the upper side and of arm-palisade tissue on the lower, Balsam canals found in the phloem of larger veins and in the soft basli of the axis. Pith cells with tanniniferous contents. Oxalate of lime occurring in the form of solitary, clustered and conglomerate crystals. Larger veins vertically transcurrent below by collenchyma. Hairy covering consisting of a few uniseriate trichomes. Cork subepidermal. Assimilatory tissue in the axis formed of chlorenchyma. Vessels large and few. Medullary rays uniseriate and numerous. Sclerenchyma enclosing the lower ends of the xylem bundles. Xylem bundles found in the soft bast. Pith characterised by numerous sievo-sclereids.

Structure of the Leaf.—The epidermal cells are horizontally tabular with inner walls gelatinised and outer walls fiat and thickened. They are secondarily divided by thin cross walls beneath which a mucilaginous mass is found. The lateral walls are thin and straight. The stomata are surrounded by ordinary epidermal cells and are more numerous on the lower surface. The guard-cells are elevated and the front cavity is on a level with the surface.

The mesophyll is composed of palisade tissue on the upper side and of arm-palisade tissue on the lower. Some of the palisade cells possess little chlorophyll and break down into cavities in dried material. Small scattered groups of sclerenchyma occur below the lower epidermis.

The internal secretory organs are represented by balsam canals in the phloem of the larger veins and in the soft bast in the axis (fig. 85 B.C.) There are numerous pith cells with tanniniferous contents. Oxalate of lime occurs in the form of solitary crystals near the veins. In the axis solitary as well as clustered and conglomerate crystals are found in cortical parenchyma, The hairy covering consists of a few uniseriate 'trichomes. External glands do not occur on the leaf and axis.

Structure of the Axis.—The epidermis consists of small tabular cells with outer walls thickened and with lateral walls thin and undulated. The cortex is composed on the outer side of cork and on the inner side of chlorenchyma.

The sclerenchymatous pericycle is not developed. The wood is composite. Vessels are few, large and arranged in incomplete rows. The interfascicular wood prosenchyma is extensive and is formed of cells with thin walls and large lumina. Small groups of sclerenchyma enclose the lower ends of the xylem bundles. The medullary rays are uniseriate and numerous. There are numerous xylem bundles in the soft bast ring giving rise to slightly ribbed appearance to the