PLANTS OF THE INDIAN DESEBT. 189 



parenchyma with numerous water-storing tracheicls. Pericycle form- 

 ed of small groups of stone-cells. Vessels small and few. Interfasci- 

 cular wood prosenchyma extensive. Medullary rays 1-2 seriate 

 Xylem bundles occurring' in the soft bast. Pith characterised by 

 sieve-sclereids. 



Structure of the Leaf. — The epidermal cells are tabular with 

 outer and inner walls convexly arched outwards and inwards respec- 

 tively. The outer walls are thickened. The cuticle is striated. The 

 lateral walls are thin and straight. The stomaU are depressed and 

 are more numerous on the lower surface and are surrounded by ordi- 

 nary epidermal cells. Guard-cells are situated in a plane a little 

 below that of the surrounding cells (figs. 82, 84). 



The mesophyll is composed of palisade tissue on the upper side 

 and of spongy on the lower. Internal glands do not occur in the leaf 

 and axis. Oxalate of lime occurs in the leaf in the form of solitary 

 crystals and clustered crystals near the veins of the leaf and in the 

 cortical parenchyma of the axis. The veins are embedded and are 

 provided with green bundle- sheaths ; they are protected on the lower 

 side by sclerenchyma. There are numerous groups of water-storing 

 tracheids with pitted markings, occurring at intervals between the 

 veins. 



The hairy covering on the leaf and axis consists of thick-walled 

 unicellular straight or bent trichomes (figs. 82, 84.) External glands 

 do not occur on th<3 leaf and axis. 



Structure of the Axis. — Epidermis 'consists of small vertically 

 tabular cells with outer walls greatly thickened and convexly arched 

 outwards. Cuticle is striated. The cortex is composed of arm-pali- 

 sade tissue on its outer side and of colourless cortical parenchyma on 

 the inner. The cortical parenchyma is distinguished by the presence 

 of sclereids with concentric stratification and radial lamellae. 



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

 wood forms a composite hollow cylinder. The vessels are small and 

 are arranged in incomplete rows. The interfascicular wood prosen- 

 chyma is extensive and is composed of thick-walled cells with small 

 lumina. The medullary rays are 1-2 seriate. A few xylem bundles 

 occur in the soft bast (fig. 83 ) and form an anomolous structure in 

 the axis. 



The pith is characterised by sieve sclereids (fig. 83) and is com- 

 posed of thick-walled cells. 



BURSERACEAE. 



Commiphora Mukul Engl— Plate XI, Fig. 85. Epidermal 

 cells of the l«aves with innerwalls gelatinised. Stomata present on 



