ROOTS 33 



plants are improved by the increased number of adventitious 

 roots caused by transplanting. Probably the whole prob- 

 lem of cuttings as compared with other means of propagation 

 rests on this question. It is also possible that with the newer 

 methods of chemically stimulating the rooting of cuttings 

 they will be more successful. A number of simple experi- 

 ments will suggest themselves to those interested. 



The structure of a root is complicated to fit it for the many 

 functions of the root system. The chief functions are ab- 

 sorption, conduction, storage, and anchorage; The younger, 

 more active and interesting parts of roots can be seen to the 

 best advantage if they are grown in a very loose, open soil, 

 from which, if they are lifted gently, the root cap and grow- 

 ing region, about one-fourth inch long, will protrude from a 

 mass of soil held around the older root by a mat of root hairs. 

 Or seeds may be germinated on moist paper where the in- 

 dividual root hairs may be seen from the smallest to their 

 normally mature size, as shown in the enlarged view of 

 Figure 11. 



Absorption is so important to the growth of plants that 

 the following chapter has been devoted to its more detailed 

 study, but it should be noted that only the younger portions 

 of roots, those without a cork layer, are permeable. Most 

 of the water and mineral salts enter the roots through the 

 root hairs shown much enlarged in Figures 9, 10, and 11. 

 They are extensions of certain of the outer cells of the root. 

 Since the root must supply these materials for the entire 

 plant, it is not surprising to find cells adapted to conduction 

 at the regions of absorption, shown best in Figure 10 as tubes, 

 collectively called xylem in the cross section of a young root 

 in Figure 9. The phloem cells, through which foods reach 

 the roots from the leaves, are less prominently developed 

 here. In older roots, the xylem is a large part of the root. 

 In perennial plants the roots continue to add to the xylem, 

 phloem, and cork areas, but the cortex may decay and dis- 

 appear. 



