PLANTS OF THE INDIAN DESERT. 101 



prosenchyma is extensive and is composed of thick- walled cells with 

 small lumen. The medullary rays are uniseriate and numerous. 

 Wood parenchyma is little developed. 



The pith consists of thin-walled cells. 



NYCTAGINACEAE. 



Boerhaavia diffusa L— Figs. 268, 269. Upper epidermis of 

 cubical cells. Lower epidermis of tabular cells. Epidermal cells of 

 the leaf and axis with tanniniferous contents. Palisade tissue on 

 the upper side and round the veins. Aqueous tissue below lower 

 epidermis. Veins with thick-walled green sheaths. Glandular hairs 

 with a uniseriate stalk and with an ellipsoidal head. Epidermal 

 cells of the axis polygonal. Pericycle formed of isolated bast fibres. 

 Endodermis of thick-walled tabular cells. 



Boerhaavia verticillata Puir.— Epidermis of both sides of 

 tabular cells. Mesophyll bifacial. Glandular hairs absent. Veins 

 without bundle-sheaths. Pericycle forming a loose ring of bast fibres. 

 Endodermis of thin-walled tabular cells. 



Boerhaavia elegans Chois.^ Fig. 270. Specific characters al- 

 most the same as those of B. diffusa. From the point of view of 

 anatomical characters it should belong to the same species. 



Structure of the Leaf. — The epidermis on the upper side of 

 B. diffusa and B. elegans consists more or less of cubical cells with 

 the outer and inner walls a little thickened. The latter are convexly 

 arched outwards. The lower epidermis in B. diffusa and B. elegans 

 and the epidermis on both sides in B. verticillata consists of tabular 

 cells with the outer walls thickened and convexly arched outwards. 

 The lateral walls are thin and straight in all members. The granula- 

 ted appearance of the outer walls is due to the deposits of crystaline 

 granules of calcium oxalate ; and the granulated walls are covered 

 by a thick cuticle. The occurrence of deposits of calcium oxalate 

 in the epidermal walls of these succulent plants protects them from 

 desiccation as well as from being easily devoured by animals on 

 account of the acrid taste. 



Stomata occur on both the surfaces and are surrounded by 

 ordinary epidermal cells. The guard-cells are situated in the plane 

 of surrounding cells and the front cavity is placed in a depression 

 formed by the upper portions of surrounding cells. 



The mesophyll in B. diffusa and B. elegans is composed of 

 palisade tissue on the upper side and about the veins and of a 

 tissue of thin-walled colourless polygonal cells with probably a water- 

 storing function on the lower side. In B. verticillata palisade tissue 



1697—14 



