42 



PRACTICAL COURSE IN BOTANY 



various ])oints near the base of the hypocotyl and spread out 

 in every direction, thus giving rise to the fibrous roots of 

 grains and grasses. 



38. Root hairs. — Notice the grains of sand or sawdust 

 that cHng to the rootlets of plants grown in a bedding of that 



kind. Examine with a lens and see if you 

 can account for their presence. Lay the root 

 in water on a bit of glass, hold up to the light 

 and look for root hairs ; on what part are they 

 most abundant? 



The hairs are the chief agents in absorbing 

 moisture from the soil. They do not last 

 very long, but are constantly dying and being 

 renewed in the younger and tenderer parts of 

 Fig. 56. — Seed- the root. These are usually broken away in 



ling of wheat, with tearing the roots from the soil, so that it is not 

 easy to detect the hairs except in seedlings, 



even with a microscope. In oat, maple, and radish seedlings 



they are very abundant and clearly visible to the naked eye. 



The amount of absorbing surface on a 



root is greatly increased by their presence. 



39. The root cap. — Look at the tip of 

 the root through your lens and notice the 

 soft, transparent crescent or horseshoe- 

 shaped mass in which it terminates. This 

 is the root cap and serves to protect the 

 tender parts behind it as the roots burrow 

 their way through the soil. Being soft 

 and yielding, it is not so likely to be in- 

 jured by the hard substances with which 

 it comes in contact as would be the more 

 compact tissue of the roots. It is composed 

 of loose cells out of which the solid root 

 substance is being formed; the growing point of the root, 

 g, is at the extremity of the tip just behind the cap, c (Fig. 57). 

 The cap is very apparent in a seedling of corn, and can easily 



Fig. 57. — Diagram- 

 matic section of a root 

 tip : a, cortex ; h, central 

 cylinder in which the 

 conducting vessels are 

 situated ; c, root cap ; g, 

 growing point. 



