128 CONSERVATIVE ORGANS. [LECT. IV. 



could be advanced, this " is perhaps/' as Mr. 

 Keith remarks, " as comprehensive as any one 

 " that can be given." 



In all plants the primary root is a simple elon- 

 gation of that part which, during the germina- 

 tion of the seed, is first protruded, and is deno- 

 minated the radicle ; but as the plant continues 

 to grow, the root gradually assumes a determinate 

 form and structure, which differs materially in 

 different plants, but is found always similar in all 

 the individuals of the same species. Botanists have 

 taken advantage of this fact, and have classed 

 roots according to their forms, as seen in the 

 adult, or fully grown root ; and have availed 

 themselves of these diversities for fixing specific 

 distinctions. The classification of roots, which I 

 have ventured to arrange, differs from that which 

 is usually found in works on the elements of Bo- 

 tany ; but it is one which, I trust, will enable you 

 to form accurate ideas regarding the structure and 

 functions of these important organs. Before, how- 

 ever, entering upon the consideration of it, you 

 ought to be informed that every root, whatever 

 may be its form, consists of two distinct parts, the 

 body, caudex, and the rootlet, radicula. The main 

 part of the root, caudex *, in trees and plants that 



* " Caudex descendens sub terra sensim subducit, et radicu- 

 " las profert, a Botanicis ex varia structura variis nominibus 

 " distinctus." Phil. Bot. 80. 



