Exercise XIV 



THE ROOT 



I. Introduction. — Except in the Psilotales, Salvinia and a few 

 specialized parasitic forms, roots are a tj'pical feature of the 

 sporophyte of vascular plants. In many of the lower tracheo- 

 phytes, the primary root is short-lived and numerous adventi- 

 tious roots soon begin development from various portions of the 

 shoot system. In seed plants, however, the radicle often reaches 

 great prominence and in such cases is termed a tai) root. Addi- 

 tional fibrous roots in seed plants arise by successive branchings 

 beginning with the first root but are also commonly formed adven- 

 titiously from the stem. Roots perform a number of important 

 physiological functions. Primarily, they serve as organs which 

 absorb water and solutes from the soil solution. In addition, 

 they are very important as structures which anchor the plant 

 firmly in the soil. The storage of reserve food material also 

 occurs in most roots to some extent and is very obviously dis- 

 played in the fleshy "roots" of carrot, beet, turnip and similar 

 econonnc plants. Although the usual environment of roots is 

 the soil, aerial roots are produced in certain vines which serve 

 to attach the shoot firmly to the surface upon which it may be 



grownig. 



1. Origin and structure of the primarif tissues of the root. 

 The primary structure of the root differs from that of the stem 

 in a number of respects. The following brief resume of these 

 differences will emphasize the salient histological eluiracteristies 

 of the root, viz. : 



(a) The structure and growth of the root apex. In marked 

 contrast to the superficial position of the terminal meristem of the 

 shoot, the root apex consists externally of a root cap which acts 

 as a protective buffer to the delicate meristem beneath it. A 

 wide variety of "types" of apical structure have been described 



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