Page:The Journal of Indian Botany.djvu/232

 ly thickened on all sides, thus adding to the rigidity of collenchyma above and below the veins of the mid-rib.

The hairy covering is composed of uniseriate trichomes (figs. 88, 93.) These are more numerous on the lower surface in Z. jujuba and Z. rotundifolia. In the other members they seem to occur on the upper surface only. Hairy covering on the axis consists of a few uniseriate trichomes as on the leaf. External glands are not found on leaf or axis.

Structure of the Axis : — The epidermis consists of small polygo- nal cells thickened on all sides. The primary cortex is characterised by the extensive development of subepidermal cork and by mucilagi- nous secretory cavities in Z. trinevia and Z. truncata.

The pericycle is composed of a composite and continous ring of bast fibres in all species except Z. jujuba, where it is represented by a composite and continuous ring of stone-cells. There are found long thin groups of stone-cells in the soft bast of Z. jujuba and Z. trinervia.

The wood forms a composite hollow cylinder in all species. The vessels are large having simple perforations and are arranged almost in complete rows. The interfascicular wood prosenchyma is exten- sive and is composed of cells with thick walls and small lumina The medullary rays are uniseriate and numerous.

The pith consists of thick-walled cells and is characterised by large mucilaginous secretory cavities. Some of the pith cells hold tanniniferous contents.

General Review : — The species of Zizyphus have the same struc- ture in the leaf and axis with certain differences which may be useful in the diagnosis of the species: —

1. Presence or absence of uniseriate trichomes on the upper surface of the leaf.

2. Shape of the upper epidermal cells.

3. Presence or absence of a groove on the upper epidermis of the mid-rib.

4. Pericycle formed of bast fibres or of stone-cells.

5. Presence or absence of stone-cells in soft bast.

Cardiospermum Halicacabum L— Fig. 95. Epidermal cells tabular with inner walls gelatinised. Stomata occurring on both the surfaces. Mesophyll formed of palisade tissue on the adaxial side and of arm-palisade tissue on the abaxial side. Cells with tanni- niferous contents in soft bast and pith. Oxalate of lime found in the leaf and axis. Leaf many-ribbed. Veins vertically transcurrent Clothing hairs unicellular or uniseriate. Glandular hairs formed of