80 SOILS AND PLANT LIFE 



of rotation not only takes into account the water-holding 

 capacity and the mellowness of the soil but also the feeding 

 requirements of the preceding crops. 



67. The Origin of Roots. — Since roots not only gather 

 moisture and dissolve mineral matter, but also conduct 

 them upward to the stems or leaves, we might be led to 

 suppose that a plant has two kinds of roots. Such is the 

 case. 



Only the young, tender portions, near the tips of the 

 roots, and the root hairs which grow out from these new 

 portions, can absorb moisture. These are known as 

 absorbing roots. 



As the root becomes older, the root hairs disappear and 

 the surface becomes covered with almost waterproof, 

 woody layers. It serves then only to hold the plant erect 

 and to conduct the moisture from the soil to the leaves. 

 Such roots are known as anchorage roots. Since they are 

 sometimes called upon to hold against the terrific force of 

 the wind, they must have a firm grip upon the roots from 

 which they grow. We shall soon see that they originate, 

 or branch, from the strong central portion of the root, 

 called the central cylinder. These anchorage roots often 

 tend to contract in length, thus fixing, or holding the plant 

 more firmly in position. The crown or rosette of leaves 

 of the dandelion, for example, which seems to be trying to 

 escape being cut off by the lawn mower, is really being drawn 

 into the soil by the contraction of its large anchorage root. 



The absorbing roots, which, as has been said, consist 

 of only the youngest portions of the anchorage roots and 

 the multitudes of root hairs which grow from them, 

 increase the absorbing surface of the young root from 

 five to twenty times. Later, as the absorbing roots become 

 anchorage roots, losing their root hairs and becoming 



