ASSIMILATION OF CARBON. 151 



If any confidence can be placed in the quantity, which may 

 be conveyed to the vegetable organs, in the form of humates, 

 crenates and apocrenates, we should infer, that when these lat- 

 ter substances were abundant, more than one third might be in- 

 troduced by these means ; but when not abundant, much less 

 than that proportion of the whole carbon which the plant 

 contains, would be furnished from the soil. So far, then, as 

 the state of our knowledge enables us to come to any just con- 

 clusions, the sources of the carbon of plants are, 



1. The carbonic acid of the atmosphere, which is the prin- 

 cipal source. 



2. The humus of the soil, or the humates, crenates and 

 apocrenates, found in vegetable mould. 



The precise quantity, from each of these sources, it is dif- 

 ficult to determine, as it will vary with circumstances ; hence, 

 we may conclude that plants, like animals, are capable of adapt- 

 ing themselves to their situation, and of obtaining, from one 

 or the other of these sources, the carbon which forms the 

 largest portion of their substance. 



Theory of the assimilation of carbon. The changes wrought 

 in the vegetable organs, upon the substances which furnish 

 carbon to plants, are, as yet, mostly matters of theory. 



We know, indeed, that carbonic acid and other substances 

 rich in carbon, are absorbed by plants, and that oxygen, ni- 

 trogen, and some other gaseous bodies, are exhaled by the 

 leaves and other green parts. But the carbon does not exist 

 in the plant in a pure state, but in combination with oxygen, 

 hydrogen and nitrogen, in definite proportions, forming the 

 vegetable proximate principles. How then is the carbon as- 

 similated ? 



The process of assimilation may be illustrated by chemical 

 transformations, although the vital power, in its mysterious 

 operations, must be resorted to, in order fully to explain the 

 phenomena. " An organic chemical transformation, is the 

 separation of the elements of one or several combinations, 



