CHAPTER III. 



VEGETAL ASSIMILATION AND DISASSIMILATION. 



1. Organic Substances. 



BEFORE speaking of the chemical transformations of which the 

 vegetal organism is the seat and the agent, it will not be useless 

 to enumerate the various bodies which penetrate into the living 

 plant from the ambient medium. 



"We have seen the roots, and sometimes the leaves, absorb 

 water, of which the plant has an imperious need. We know 

 that the water absorbed by the roots is loaded with substances 

 in solution. Among these substances, some are terreous, and we 

 shall pass them under review at a future time in this exposition 

 (salts of lime, soda, potash, ammonia, &c.). It is through the 

 roots that the larger part of the azote which is necessary to the 

 plant penetrates into it. This azote is introduced into the plant 

 in the form of salts of ammonia and especially of a series of 

 substances produced from the slow oxydation of the organic 

 detritus. The type of these substances is a compound of C 40 , 

 H !6 , O 14 , ulmine, which, according to Miilder, is transformed by 

 a gradual sur-oxygenation into ulmic acid, humine, humic and 

 geic acids, &c. The acids of this series eagerly absorb ammonia, 

 and compose with it soluble salts. They form also soluble 

 alkaline salts, and terreous salts, which would be insoluble if the 

 ammonia did not form therein an aggregation of double salts. 

 According to Miilder, water co-operates with these formations, 



