412 CONSERVATIVE ORGANS. [LECT. VIII. 



the absorbent mouths of the root, and must either 

 possess a valvular apparatus, or a power of c,on- 

 tracting strongly, so as to enable them to retain 

 the fluid they imbibe, until it is taken up by 

 the ligneous vessels. From their forming on 

 the radicles and their divisions, and seldom or 

 never on the caudex, they are placed at a dis- 

 tance from the trunk of the tree ; and conse- 

 quently seeds and small plants thrive better close 

 to trees, than at a little distance, the earth being 

 less exhausted in the vicinity of the larger roots 

 than where the radicles spread. 



I have already stated (p. 129) the opinion of 

 Du Hamel and some other phytologists, re- 

 garding the annual death and reproduction of 

 the fibrils ; and the objections to it urged by Mr. 

 Knight. My own observations induce me to be- 

 lieve that fibrils are annual productions in all de- 

 ciduous trees and shrubs, although they are 

 perennial in evergreens. Were I called upon to 

 suggest a reason for this distinction, I would say, 

 that, as the fibrils do not appear until the leaves 

 begin to expand, they are produced for the pur- 

 pose of maintaining a due balance between the 

 absorption and the exhalation of the plant, and to 

 secure a supply of nutriment in proportion to the 

 demand, which must always depend on the energy 

 of the leaves in which it is converted into the 

 proper juice of the plant ; and, therefore, when the 



