Ch. V, 1] 



FEATURES OF ROOTS 



213 



where often it is used for storage of food. That the mass 

 of roots keeps towards the surface, especially in the largest 

 plants, is due in part to the need for aeration, and in part to 

 the increasing hardness of the soil with greater depth. 



In size, roots bear close relations to shoots, for it is clear 

 that the shoot takes the lead, so to speak, in determining the 

 form and habits of the 

 plant, and secondarily 

 produces a corresponding 

 quantity of roots. No 

 matter what the size at 

 the trunk, all roots end in 

 the delicate white tips de- 

 voted to absorption and 

 growth ; and in correlation 

 with this uniform function, 

 performed under compara- 

 tively uniform conditions, 

 the tips of typical soil roots 

 are not far from one size. 



In texture, roots vary 

 from woody-hard in trees 

 (the wood, indeed, of roots 

 being often harder and 

 more compact than that of 

 the stems) down to the 

 softness of meristem in 

 growing tips. The fibrous 

 parts are tenaciously tough, 

 — a quality which is evi- 

 dently connected with the fact that the anchorage function 

 of the roots falls largely on the fibers. 



In color, roots are white at their growing tips, that being 

 the natural color of meristematic tissue. Farther back they 

 are brown, from the development of protective cork ; and 

 in older parts they are very dark from the action of the 



Fig. 156. — A typical root system, of 

 Corn. (From Bailey.) 



