48 THE VEGETATIVE ORGANS 



Absorption by Roots 



Root-hairs the organs of absorption. If young roots, 

 bearing root-hairs, are examined by means of a pocket lens 

 or under a microscope, it will be seen that each root -hair 

 consists of a long, tubular outgrowth of an epidermal cell 

 (see Fig. n, 7, e). The wall (c.w) consists of a thin mem- 

 brane of cellulose, the substance of which the fibres of 

 cotton are composed. The outer exposed surface is some- 

 what slimy, and to this the soil-particles adhere firmly. 

 Within the tube is the living substance known as proto- 

 plasm (p), together with a little rounded body the nucleus 

 (n). The protoplasm forms a thin living lining to the tube ; 

 and from the lining, strands of protoplasm stretch across 

 the cavity. The centre of the tube is occupied by sap. 

 Farther back, in the older parts of the root, the surface 

 tissues are corky and no root-hairs are found. Root-hairs 

 are also absent from the region protected by the root -cap. 

 That part of the young root which bears root-hairs is called 

 the root-hair region. 



The different regions of a root are strikingly shown in 

 a plant which a gardener would describe as ' pot-bound ', 

 i. e. a plant which has grown so long in a pot that its roots 

 have spread themselves out in a tangled mat between the 

 soil and the pot. On turning out such a plant numerous 

 tender, white roots, crowded with root-hairs, are found 

 covering the surface ; while the roots buried in the soil 

 are tough, wiry, and covered with a firm brown layer of 

 cork. 



What are the uses of these different parts ? The root- 

 cap doubtless serves to protect the young growing root as 

 it pushes its way through the soil. The older parts, sur- 

 rounded and protected by cork, are no longer able to 

 absorb water, but they fix the plant in the soil and bear 

 at the ends of their branches the tender roots clothed with 



