Di' Seller on the Ntitntion of Plants. 63 



Heving, that plants, especially in warm climates, derive part, 

 at least, of their nitrogen from the nitric acid of nitrates ex- 

 isting in the soil. 



As respects, then, the supply of nitrogen to plants, it is 

 impossible to agree with Liebig farther than that ammonia 

 is part of the food of plants. For a completely definite opin- 

 ion the time has not yet arrived ; but the interest given to 

 this so long neglected subject by Liebig's affirmations, can- 

 not but ensure its complete elucidation within a short period. 

 This part of the subject I conclude with two propositions, 

 which deserve the strictest examination. 



\st, That ammonia is produced in the soil during the de- 

 composition of parts of plants containing no nitrogen, — the 

 nitrogen being, according to Berzelius, derived from the air ; 

 and, 2d, in a decomposing mass of animal matter, that the 

 nitrates first formed from the nitrogen of the animal matter, 

 contrary to the common belief of chemists, induce, catalyti- 

 cally, the production of nitrates from the nitrogen of the air. 



The last axiom drawn from Liebig's work, on which I pro- 

 posed to comment, is, that the saline matters contained in 

 plants are drawn exclusively from the soil, and are in no re- 

 spect the product of vegetation. On this subject I must be 

 more brief than I intended. 



The ashes of plants, though not absolutely constant, ai'e 

 nevertheless in so far constant, as to shew that a certain 

 saline constitution belongs, in its most noi-mal and healthy 

 state, to every species. Two difficulties present themselves 

 in the investigation of this subject, namely, the substitution, 

 by a kind of isomorphism, of one substance for another under 

 peculiar circumstances ; and the presence, on most occasions, 

 of saline matters which are not essential but accidental. The 

 general principle, as respects the saline constitution of plants 

 taught by Liebig, is sufficiently made out, but the subject has 

 been as yet too little studied in its details. The subject is, 

 indeed, clear enough to a certain extent ; but, until the whole 

 of the respective offices of the inorganic and organic portions 

 of the soil be made apparent, some doubts must hang over 

 our conclusions. 



Forms of potass and phosphates of a few bases, the most 



