ROOTS AND THEIR USES 



173 



Fig. 107. — Vegeta- 

 tive multiplication by 

 layering. A portion of a 

 living stem was covered 

 with soil and adventive 

 roots have grown from 

 the covered portion. 



buried part, adventive roots grow itito the ground (Fig. 



107), and when the connection with the parent plant is 



broken, the new roots with the adjacent 



bud or buds form a new plant. The 



slender canes of the black raspberry, if 



allowed to grow long, bend over to the 



soil of their own weight and so perform 



the operation of layering for themselves. 

 195. Work of Roots : Absorption. — 



The different forms that roots take are 



closely connected with the kind of work 



that they have to do. The work of 



roots is of various kinds ; it differs much 



with the location, size, and habit of the 



plant. Much has already been said of 



the part that roots play in absorbing, usually from the soil, 



water and certain other substances that the plant needs. 



Since absorption goes on through the root hairs, and since 



these are short-lived and are borne only on the younger 

 parts of each root, it is necessary that 

 the root should continue to grow so 

 that there shall always be a young 

 region supplied with root hairs. 



If the plant Uves and grows for 

 many years, the roots must continue 

 to grow and branch, so that, as the 

 parts of the plant above ground need 

 more and more water, the root hairs 

 may increase in number and may 

 come into contact with a larger area 

 of soil. The growth of the roots also 

 brings them into deeper layers of the 



soil where there is likely to be a more steady supply of water. 



These are among the reasons why long-lived plants need 



much-branched root systems, composed of long but relatively 



Fig. 108. — Root hairs 

 of the barley. 



