72 PLANT LIFE 



is impossible completely to wash the soil away 

 from this portion. Still further behind, the 

 soil ceases to adhere to the surface. Other 

 roots or rootlets are seen to be growing out, 

 and still further away from the tip the 

 diameter of the young root begins evidently 

 to increase. Thus we distinguish four regions : 

 (1) the tip and clean surface; (2) the hairy 

 zone ; (3) the region from which young rootlets 

 are springing ; (4) The older parts which are 

 getting thicker. 



The only part of the root which is actively 

 absorbing water from the soil is the hairy 

 zone, and the hairs themselves outgrowths 

 from the superficial cell layer are the essential 

 structures which perform this task. The apex 

 is chiefly concerned with boring on through 

 the soil, and it is covered with a characteristic 

 covering of cells called the root-cap, the outer 

 cells of which are continually being worn away 

 by attrition in the soil, and as constantly being 

 replaced by the formation of fresh layers from 

 within. The superficial cells behind the 

 region of the root-cap do not begin to elongate 

 at once to form hairs. This does not happen 

 till the part of the root from which they 

 spring has ceased to elongate. The meaning 

 of this at once becomes clear when we reflect 

 that these delicate protuberances, the root- 

 hairs, are in very intimate contact with the 

 particles of soil and if the part of the root 

 which bears them were to continue to grow 

 in length, they would be torn away from their 



