Dr Seller on the Nutrition of Plants. 51 



Liebig on the nutrition of vegetables, for the purpose of de- 

 termining how far these are just, and with what limitations 

 they require to be received. 



The following propositions represent the spirit of the 

 opinions on which I wish to comment. 



1*^, That the food of plants is strictly of a mineral or in- 

 organic nature. 



2d, That ammonia, carbonic acid, and water impregnated 

 with a few saline matters, are the sole aliments of plants. 



2d, That the organic matter of soils must pass into the 

 mineral state, namely, into water with a saline impregnation, 

 carbonic acid and ammonia, before it can become subservient 

 to the uses of vegetation. 



4:th, That the saline matters and the like, which form the 

 ashes of plants, are, without exception, taken up from the 

 soil, and are, in no respect, the product of vegetation, as 

 was taught in the beginning of the present century. 



Thus the maxims adopted by Liebig on the nutrition of 

 plants are of a negative character ; for, if it can be shewn 

 that the doctrine of the nutrition of plants by organic com- 

 pounds in the soil is unfounded, then the truth of Liebig's 

 grand axiom, as to the mineral natm^e of the food of plants, is 

 established at once. 



There are two gi'oups of opinions to which those of Liebig 

 stand in a negative relation, namely, those which represent 

 the food of plants as solely or principally of an organic kind, 

 and those again which admit the food to be inorganic in the 

 main, yet available for nuti'ition only when certain azotised 

 matters of an organic nature, derived from the soil, are present. 



It is the first of these two groups of opinions only, that 

 stands opposed in particular to what Leibig inculcates, and 

 to this I propose to address myself chiefly ; for, unless all 

 opinions of this stamp be overthrown, it is impossible to sub- 

 scribe to his doctrine. 



If the food of plants be solely organic substance, then 

 there must have been originally (or at least at one time*) in 



* To assume that soil was formed from the atmosphere in the course 

 of time, by the gradual rise of the vegetable kingdom, would be to beg the 



