116 ACTION OF SALTS. 



zed upon, and becomes inert. Nitrates act under the 

 influence of the growing plant, the base let loose acts 

 on geine, the acid is decomposed, and nitrogen given 

 up to the plant, and it becomes one of their essen- 

 tial elements. The elements of nitrate of ammo- 

 nia are all taken up both acid and base. If there 

 are any salts which can be called vegetable food, 

 they ate the nitrates. The organic constituents of 

 plants, are hydrogen and oxygen, carbon and nitro- 

 gen. The two first form water ; the two middle 

 carbonic acid, the first and last, ammonia. Water, 

 ammonia, and carbonic acid then, or their elements, 

 compose the organic part of all plants. Water and 

 carbon exist in the first division, and nitrogen in the 

 second division of geine, which thus contains the ele- 

 ments of water, ammonia and carbonic acid, or the 

 whole food of plants. The nitrogen, also, exists in 

 the air. It forms 80 per cent, of it. In this state it 

 cannot be assimilated by the plant till that has put 

 forth its leaves. Its only source for the roots and for 

 the germinating seed, is that arising, either from the 

 geine, or from the ammonia evolved by the ferment- 

 ing dung, or from nitrates. In either case, whether 

 the nitrogen arises from the geine or from the nitrates, 

 decomposition takes place, by the action of the living 

 plant. 



