CHAPTER XII 



THE ROOT 



As has been indicated in the preceding chapter, the root is 

 characterized by the possession of a protective terminal structure 

 known as the root cap, by its radial organization, and by its endoge- 

 nous or internal mode of origin. The first and the last charac- 

 teristics are exclusive features of the root, but that of radial 

 organization is often 

 present in stems of 

 the more primitive 

 types. A comparison 

 of the upright stem of 

 the common club 

 moss, Lycopodium 

 clavatum, with the 

 root of the same 

 species makes the 

 truth of this state- 

 ment particularly 

 apparent. It is clear 

 from Figs. 100 and 

 101 that the radial 

 organization is com- 



FIG. 100. Transverse section of the root of 

 Lycopodium clavatum. 



mon to the two 

 organs and that they 

 differ only in the fact 



that the stem bears leaves. This resemblance in anatomical 

 structure between stem and root is often present in the lower 

 Lycopodiales and furnishes a strong argument, taken together 

 with their ancient occurrence and early decline as a prominent 

 element of the earth's vegetation, for the view that the lycopods 

 are the most primitive plants. 



In the great majority of vascular plants the contrast between 

 the organization of the stem and that of the root is very striking. 



143 



