60 Dr Seller on the Nutrition of Plants. 



proportion of carbon derived from the soil. This point, also, 

 deserves farther examination. 



The source of the nitrogen of plants is, according to Liebig, 

 exclusively from ammonia accumulated in the soil. He re- 

 fuses to believe that the nitrogen of the air enters into the 

 constitution of plants, either directly, in its simple state, or 

 indirectly, by passing first into ammonia. This is a topic of 

 the very last importance, and is the principal novelty in 

 Liebig's view of the nutrition of vegetable bodies. 



The ammonia that serves for food to plants is, according 

 to Liebig, originally of mineral origin ; for example, from 

 volcanic sources. This ammonia passes into the azotised 

 parts of plants, especially into those destined to be the food 

 of animals ; and this is the som*ce of the abundant nitrogen 

 of the animal kingdom. The excretions of animals, and the 

 decomposition of animal and vegetable substances, restore 

 this ammonia to the soil, or, if it has escaped into the air, it 

 is brought back by rains ; in either case to pass through the 

 same circuit. 



This view of Liebig's will hardly stand the same kind of 

 test to which the idea of organic matter being the sole food 

 of plants was subjected above. For, if his opinion be correct, 

 the amount of organic life on our globe must be limited by 

 the quantity of ammonia existing at the surface ; it never 

 can pass the limit fixed by the quantity of ammonia. 



If, then, there be any waste of ammonia, if there be any 

 portion of the nitrogen of plants or animals (both equally by 

 hypothesis derived from this source) which does not return to 

 the state of ammonia, there must be a gradual extinction of 

 the organic world, like what was before referred to in the 

 case of carbon. The only alternative is, that the volcanic, or 

 other similar sources of ammonia, shall be shewn to be in 

 constant operation, so as to compensate for the whole waste 

 here supposed. 



But it is impossible that there should not be in nature a 

 great annual waste of ammonia, — that is, a great annual 

 decomposition of it into its mineral elements, or into that 

 form under which, according to Liebig, its nitrogen cannot 

 directly or indirectly avail for the nutrition of plants ; nor 



