THE STRUCTURE OF THE ROOT 31 



of the numerous rootlets, spread through so much of 

 the earth, aided very conspicuously by the large net- 

 work which the branches form; and a very large area 

 of water-covered particles is tapped by the absorbing 

 root hairs the rootlets bear. 



As the system gets older, not only is it continually 

 enlarged by the increased branching, but the individual 

 roots and branches increase in girth and press more and 

 more firmly into the soil. They penetrate very deeply 

 and extend laterally very widely, so that with the in- 

 creasing size of the above-ground portion of the plant a 

 firmer and firmer anchorage is afforded, securing the 

 needed stability. 



CHAPTER IV 



THE STRUCTURE OF THE ROOT 



THE internal structure of the root can be properly 

 understood only when it is studied from the point of 

 view of the work which the root has to do. At its first 

 emergence from the seed its substance is composed of a 

 large number of the vegetable cells which we have 

 described, each a little mass of protoplasm separated 

 from its neighbours by delicate cell walls. They are in 

 close contact with each other at all points and have no 

 cavities in them. The chief difference in the mass is 

 that the external cells at the apex form a kind of cap 

 over the tip of the radicle, so that its actual apex is not 

 exposed. This cap protects the true apex from damage 

 as it penetrates into the soil. When the radicle has 

 begun to elongate changes in the cells are set up. If a 

 longitudinal section of it (Fig. n) is examined these 

 changes will be seen to separate the young root into 

 roughly three areas. The cap can be seen in front, a 

 short region behind it shows the cells small and actively 



