Page:The Journal of Indian Botany.djvu/128



Tamarix dioica Roxb. — Pl. VI, fig. 45. Epidermal cells with inner walls a little more thickened than outer walls. Pits not deep. Cortical parenchyma of small cells. Sclerenchymatous pericycle more or less forming a loose ring of stone-cells with interposing cells thickened and radially striated. Wood forming a composite hollow cylinder. Soft hast forming groups. Medullary rays 2-6 seriate. Pith composed of thick-walled cells.

Tamarix orientalis Forsk.— Fig. 46. Epidermal cells with outer and inner walls thin. Pits quite deep. Cortical parenchyma formed of large thin-walled cells. Sclerenchymatous pericycle more or less isobilateral. Wood forming a composite central cylinder without a central pith tissue. Soft bast forming a continuous ring. Medullary rays uniseriate and few.

Structure of the Axis:—The epidermis consists of thin- walled horizontally tabular cells. The front cavity is depressed and closed above and below by thin walls, fig. 45. The guard-cells are in the plane of or in a plane lower than that of the surrounding cells.

Clothing hairs are not found on the axis of either of the species. External glands, figs. 45, 46, are placed in pits ; they form spherical structures divided by horizontal and vertical three-wall into four thin-walled cells, and are. accompanied on their inner side by two depressed epidermal cells which form the subsidiary cells of the glands. The glands do not project above the surface; they secrete hygroscopic salts which fill the pits and absorb moisture from the air outside.

The primary cortex is characterised on its outer side by an assimilatory tissue of palisade cells and on its inner side by cortical colourless parenchyma. There are numerous water-storing tracheids in the cortical parenchyma with pitted or scalariform thickenings, the larger ones being accompanied by a few stone-cells. Cortical parenchyma forms an aqueous tissue and in T. orientalis is composed of large thin-walled cells.

The pericycle is composed of large groups of stone-cells. The stone-cell groups in T. dioica are closely placed all round the soft bast and the cells interposed between them are characterised by sclerosis and by radical striation of the wall. In T. orientalis stone-cell groups are placed on two opposite sides in the form of arcs and the cells interposed between them are thin-walled and parenchymatous. The sides possessing the stone-cell groups may perhaps represent the plane of the axis most affected by the wind ; and the stone-cell groups may have been developed in that plane to protect the axis against violent shaking by the wind.