PLANTS OF THE INDIAN DESEET. 287 



with acicular raphides (fig. 160) in the assimilatory tissue in the leaf 

 and axis. Besides these, there are assimilatory cells in the mesophyll 

 with tanniniferous contents (fig. 160 G.). 



Oxalate of lime occurs only in S. hispida either in the form of 

 acicular raphides in the mesophyll and pith (fig. 161 A. E.), or in the 

 form of crystal sand in the cortex. The vains are embedded and are 

 not provided with bundle-sheaths. "Veins of the mid-rib are vertically 

 transcurrent above and below by collenchyma in 0. aspera. 



The hairy covering on the leaf and axis in S. hispida (figs. 160, 

 161) consists of articulate uniseriate trichomes with the terminal cell 

 ending in a sharp point ; trichomes on the axis are situated in groups 

 on the wiug-like ribs at the angles (fig. 161). Trichomes are more 

 numerous on the lower surface of the leaf. Clothing hairs are absent 

 on the leaf of 0. aspera ; on the axis, however, there are peculiar 

 dome-like unicellular hair-like structures with walls thickened and 

 muriculate. Glandular hairs are not found on the leaf and axis. 



Structure of the Axis. — The epidermis consists of tabular cells 

 with outer walls greatly thickened. The outer walls are muriculate 

 and the inner walls also thickened in 0. aspera (fig. 162). The lateral 

 walls are thin and straight. There are large wing-like ribs at the 

 angles of the axis in S. hispida. The cortex of S. hispida is composed 

 of parenchymatous assimilatory tissue extending into ribs which 

 are strengthened by collenchyma. Assimilatory cells contain rounded 

 bodies of the nature of fat bodies. Endodermis is differentiated. 

 Sclerenchymatous pericycle is found only in S. hispida and is com- 

 posed of a loose ring of bast fibres. 



The vessels are arranged in complete rows and are larger in the 

 lower half of the wood. Interfascicular wood prosenchyma is scantily 

 developed and is formed of cells with thin walls and with large lumina. 

 Medullary rays are uniseriate and numerous. The abundance of 

 vessels and the scanty development of interfasicular wood prosencby 

 ma are characteristic of the herbaceous nature of the plants. 



The pith is composed of thin-walled cells. 



{To be continued.) 



