4 THE JOURNAL OF INDIAN BOTANY. 



(fig. 163) and D. tomcntosa (fig. 186) ; secretion collects below the 

 cuticle which is swollen like a bladder. Besides the biseriate spheri- 

 cal glands, there are other glandular hairs on the axis of P. scncgalcnsis, 

 which are composed of a long, broad, biseriate stalk and of a small 

 biseriate head (fig. 170) ; there are also peculiar hairs with a long 

 multicellular stalk and with a small biseriate head, occurring in groups 

 on the lower side of the mid-rib of the leaves (fig. 169). External 

 glands are more numerous on the lower surface of the bifacial leaves ; 

 they check transpiration by pouring their secretion on the surface. 

 The greater abundance of stomata on the lower surface brings about 

 the development of a dense covering of clothing and glandular hairs 

 on the lower surface. 



Structure of the Axis. — The epidermis is one layered, the outer 

 and inner walls being equally thickened. The former are convexly 

 arched outwards. Lateral walls are thin and undulated. Guard- 

 cells are elevated and the front cavity is on a level with the surface 

 in P. angustifolia, E. echinatus, D. tomenlosa (fig. 188) and L. chon- 

 drilloides ; in other members guard-cells are situated in the same 

 plane as that of the surrounding cells and the front cavity is situated 

 in a depression produced by outer thickened epidermal walls. The 

 elevated position of the stomata is necessitated by the abundance of 

 thin-walled cortical parenchyma. 



The primary cortex is characterised by the assimilatory tissue 

 formed either of palisade tissue as in L. chondrilloides or of chloren- 

 chyma as in other members. Collenchyma is developed in the ribs 

 of E. echinatus, V. divaricata and D. tomcntosa, while in P. raj put- 

 anae (Fig. 189 CI) there occurs a continuous sub-epidermal ring of 

 collenchyma. Endodermis is differentiated in P. senegalcnsis, E> echi. 

 natas and I). tomcntosa (fig. 189), and it consists of thin-walled tabular 

 cells with perhaps a water-storing function. 



The pericycle consists of a more or less composite ring of groups 

 of stone-cells with small lumina in all members except in E. echinatus, 

 where it is formed of stone-cell groups separated by bast fibres (fig. 

 182). The arrangement of stone-cell groups in D. tomcntosa is isobi- 

 lateral, larger groups being developed on the side exposed to the direc- 

 tion of the prevailing winds. 



