32 



SOUTH INDIAN GRASSES 



Fig. 45. — Transverse section of the entire root of 

 Andropogon Sorghum. x 25 



To learn the structure of the roots of grasses we may select as 

 types the roots of Pennisetum cenchroides and Andropogon Sorghum 

 and consider their structural details. In the transverse sections of 



these roots we find 

 a fairly broad 

 cortex consisting 

 of thin-walled 



parenchymatous 

 cells more or less 

 regularly arranged. 

 (See figs. 44 and 

 45.) Just below the 

 piliferous layer two 

 or three layers of 

 thick-walled cells 

 are seen. In the 

 roots of Andropogon 

 Sorghum these 



thick-walled cells 

 are very conspi- 

 cuous as they con- 

 sist of several 

 layers. These 



layers of thick- 

 walled cells consti- 

 tute the exoder- 

 mis. (See fig. 46.) 

 The innermost 



layer of cells of the cortex is called the cndodcrmis and it becomes 

 conspicuous on account of the thickening in the lateral and inner 

 walls of the cells of this layer. (See figs. 44 and 47.) 



The rest of the root form- 

 ing the central core is the 

 stele and at its periphery 

 there is a single layer of 

 cells called the pcricyclc. 

 The arrangement of the 

 xylem and the phloem is 

 different from that of the 

 stem. They lie side by side 

 on different radii, and not 

 one behind the other on the 

 same radius as in the stem. 

 The number of xylem 

 groups is fairly large and 

 the development of the 

 xylem is from the pericycle 

 towards the centre of the 

 stele. (See figs. 44 and 45.) 

 The parenchymatous cells 

 in the centre of the stele 

 become thick-walled in 

 older roots. 



Structure of the leaf. — The structure of the leaf of grasses is 

 quite characteristic of the family. In every leaf a number of 



Fig. 46. — Transverse section of the cortica 



portion of the root of Andropogon Sorghum. 



x 150 



r.h. Root-hair ; p.l. piliferous layer ; 



ex. exodermis ; co cortex. 



