102 THE JO0KNAL OF INDIAN BOTANY. 



occurs on the upper side ; and there is an extensive tissue, occupying 

 two-thirds of the portion of mesophyll, of thin-walled polygonal cells 

 faintly green in colour and partly functioning as an aqueous tissue. 



Internal secretory organs are represented by epidermal cells, with 

 tanniniferous contents, of the leaf and axis of B. diffusa and B. elegans. 



Oxalate of lime, besides being deposited in the form of granules 

 in outer epidermal walls, occurs in the form of bundles of raphides 

 and of crystal sand in mesophyll of leaves and in the primary cortex 

 of the axis of all members. Granular deposits in the outer epidermal 

 walls are abundant and give to the surface of the leaf and axis a 

 whitish appearance, which besides protecting these succulent plants 

 from being easily devoured by animals on account of the acrid taste, 

 reflect light and arrest transpiration. 



The veins are embedded and are enclosed in thick-walled green 

 bundle-sheaths in B. diffusa and B. elegans. Bundle-sheaths are not 

 found in B. verticillata. 



The hairy covering consists of glandular hairs and occurs on the 

 axis and both the surfaces of the leaf of B. diffusa and B. elegans. The 

 glandular hairs (tig. 268) are composed of a uniseriate long stalk and 

 of an elongated and ellipsoidal head. The cells of the stalk become 

 narrower towards the apex. External glands are not found in B. verti- 

 cillata. 



Structure of the Axis. — The epidermal cells in B. diffusa are poly- 

 gonal, while those in B. verticillata are tabular. The outer walls are 

 thickened, convexly arched outwards and granulated with deposits of 

 calcium oxalate. The primary cortex (fig. 269) is composed of collen- 

 chyma on its outer side and of chlorenchyma on the inner side. The 

 endodermis is distinct and is composed of tabular cells which are 

 thick-walled in B. diffusa and B. elegans. 



The pericycle consists either of isolated bast fibres as in B. diffusa 

 and B. elegans or of a loose ring of bast fibres in B. verticillata. The 

 wood is characterised by the occurrence of two rings of xylem bundles. 

 The primary bundles are small and are embedded in a thin ring of 

 interfascicular wood prosenchyma which is composed of cells with 

 thick walls and with small lumen. The secondary bundles are irre- 

 gularly arranged in the pith and are separated by broad strips of thin- 

 walled parenchymatous cells, resembling medullary rays. Soft bast is 

 found in groups on the outer side of xylem bundles. 



The pith tissue between the primary and secondary vascular bun- 

 dles consists of cells with thickened and lignified walls and filled with 

 granular contents, and that between and enclosed by the secondary 

 vascular bundles is formed of very thin-walled cells. 



