PLANTS OF THE INDIAN DESERT. 161 



Structure of the Leaf. — Epidermal cells are polygonal with outer 

 walls thickened and papillose on both the sides in C. polygonoides 

 and on the upper only in 1 P. plebejum. Epidermal cells on the upper 

 side in the latter are tabular with outer walls thickened and flat. 

 Large water-storing cells are intercalated amongst ordinary epidermal 

 cells in P. plebejum. Lateral walls are thin and undulated. 



Stomata are surrounded by ordinary epidermal cells and are 

 equally numerous on both the surfaces. Guard-cells are in the plane 

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

 formed either by outer thickened epidermal walls or by the papillae. 



Mesophyll is isobilateral in G. polygonoides, while in P. plebejum 

 it consists of palisade tissue on the upper side and of arm-palisade 

 on the lower. There is a tissue of polygonal cells with tanniniferous 

 contents in the middle of the mesophyll in G. polygonoides. 



Internal secretory organs are represented in G. polygonoides by 

 polygonal cells in the middle of the mesophyll and by palisade-like 

 cells, in the palisade tissue, with tanninifarous contents. Sheath- 

 cells in P. plebejum hold tanniniferous contents. Oxalate of lime 

 occurs in the form of clustered crystals in the mesophyll of P. 

 plebejum. 



Veins are embedded and are enclosed in bundle-sheaths. Sheath- 

 cells in P. plebejum hold tanniniferous contents. 



Hairy covering, in G. polygonoides, consists of uniseriate trie- 

 homes which are composed of a basal cell and of a terminal cell with 

 verrucose walls and more or less adpressed. External glands in 

 C. polygonoides are club-shaped and consist of a biseriate short stalk 

 and of a head irregularly divided. 



Structure of the Axis. — The epidermis consists of small polygonal 

 cells with outer walls thickened and papillose, thickening being con- 

 siderable in G. polygonoides. Outer walls are granulated in P. plebe- 

 ium. Lateral walls are thin and undulated. Some of the epidermal 

 cells in C. polygonoides hold tanniniferous contents. The primary 

 cortex is characterised by an assimilatory tissue of palisade cells. The 

 mechanical tissue is represented by sub-epidermal strands of collen- 

 chyma and of stone-cells in the ribs of P. plebejum and C. polygonoid- 

 es respectively. Along almost one-third of the circumference of the 

 axis, cork is developed below epidermis. This suggests that the 

 axis is greatly inclined and that cork is developed on the upper side 

 which is exposed to the sun. Endodermis is differentiated and is 

 characterised by tanniniferous contents in the species of both the 

 genera. The pericycle is composed of small groups of stone -cells 

 (figs. 292, 293). Stone-cell groups in C. polygonoides are radially 

 much elongated. Cells interposed between stone-cell groups are 



