570 



Miscellaneous. 



ally Saintfoin and Lucern, form such excretions abundantly, and 

 continue to do it for several years in succession." From this the 

 reader would probably infer, that no plant can thrive where Clover 

 has been grown; but Dr. Liebig does not draw such a conclusion. 

 It is well known that many plants grow in the midst of, and almost 

 immediately after. Clover, at least what are commonly called weeds. 

 According to Liebig's first and second chapter, humus in no 

 way contributes to the nutrition of plants ; nevertheless he here 

 tells us, that one of the principal effects of the rotation of crops 

 is the artificial production of humus, which is most completely 

 obtained by the cultivation of Saintfoin and Lucern." Alas ! for 

 the poor farmer, who is to borrow the theory of his art from 

 Dr. Liebig's book. But, to proceed : " It is evident," says Liebig, 

 " that after from five to seven years the soil must be impregnated with 

 excretions to such a degree, that all the roots wiU be surrounded by 

 them ; and as they remain for some time in a soluble condition, they 

 are again introduced into a plant, which suffers injurious effects 

 in consequence, because they are not capable of being assimilated." 

 Dr. Liebig does not consider that roots extend, and that food 

 enters them only by their extremities. This extremity, which is 

 to receive nutrition, is annually leaving the place which, according 

 to his theory, is poisoned with these pretended excretions, and it 

 extends into a soil which is free from them. Sometimes these 

 extremities advance over a considerable space in a short time. 

 I think, therefore, that the bare places found in a field of Clover, 

 after 5 or 7 years, are not produced by the roots refusing a soil im- 

 pregnated with excretions, but that the life of such plants has arrived 

 at its term, and that they could not continue to vegetate even in the 

 best soil. If excretions were the cause of this change, the whole 

 field would be depopulated at the same time ; but we find that it is 

 only single plants that die, and thus, according to the difference 

 of their qualities, become sooner or later extinct. Thus bare places 

 are formed on the field of Clover, but these places do not remain 

 without vegetation until again converted into humus by the sun 

 and atmosphere ; on the contrary, even before the Clover has entirely 

 died, they are covered with small plants, which thrive very well. 



