194 THE JOURNAL OF INDIAN BOTANY. 



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 Bevieio : — 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. 



SAPINDACEAE 



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 



