PLANTS OF THE INDIAN DESERT. 247 



beneath and grooved above. The smaller veins are enclosed in a 

 sheath of cells, some with mucilaginous membranes and others with 

 clustered crystals. The larger veins are vertically transcurrent 

 above by coilenchyma. 



The hairy covering is dense and consists of clothing hairs on the 

 leaf and axis. The clothing hairs are unicellular, long and woolly figs. 

 122, 124 ; they are more numerous on the lower surface of the leaf. 



Structure of the Axis : — The epidermis consists of polygonal cells 

 with outer walls thickened and papillose. The inner walls are thick- 

 ened ; the lateral walls are thin and undulated. 



The cortex fig. 124 is composed of coilenchyma on the outer side 

 and of an extensive tissue of thin-walled colourless cells on the inner 

 side with perhaps occasionally a water-storing function. Cells at the 

 inner margin of the cortex have mucilaginous membranes. 



Sclerenchymatous pericycle is not developed. The wood is com- 

 posed of large xylem bundles separated by broad medullary rays 

 some of the cells of which have mucilaginous membranes. Interfasci- 

 cular wood prosenchyma is not developed. 



The pith cells towards the periphery are mucilaginous. 



LYTHRACEAE 



Ammania baccifera L. — Fig. 125. Epidermis formed of thin- 

 walled tabular cells. Clothing hairs absent. Oxalate of lime not 

 found. Pericycle formed of bast fibres, with thin walls and large 

 lumina. Small groups of thick-walled cells found in the pith formed 

 of thin-walled cells. 



Ammania desertorum Blatt. & Hall— Fig. 126. Epidermal 

 cells tabular with outer walls thickened and convexly arched outwards. 

 Clustered crystalls found near the veins. Conical unicellular hairs 

 with verrucose walls occurring on the axis and on the upper surface 

 of the leaf. Pericycle formed of bast fibres with thick walls and with 

 small lumina. Pith composed of thin- walled cells. 



Structure of the Leaf : — The epidermal cells in A. baccifera fig. 

 125 are tabular and thin-walled except at the margin where the outer 

 walls are thickened and convexly arched outwards. In A. desertorum 

 the epidermal cells have the outer walls thickened and convexly 

 arched outwards. The cuticle is striated. The lateral walls are thin 

 and straight. The margins are curved downwards. 



Stomata are more numerous on the lower surface and are 

 surrounded by ordinary epidermal cells. Guard-cells are elevated and 

 the front cavity is on a level with the surface figs. 125, 126. The 

 stomata on the axis are similar to those on the leaf. 



{To be continued) 



