THE pLA^rr. 25 



subject, also the means for retaining in the soil the 

 ammoniacal parts of fertilizing matters, will be fully 

 considered in the section on manures. 



After ammonia has entered the plant it may be 

 decomposed, its hydrogen separated from it, and its 

 nitrogen retained to answer the purposes of growth. 

 The changes which nitrogen undergoes, from plants 

 to animals, or, by decomposition, to the form of am- 

 monia in the atmosphere, are as varied as those of 

 carbon and the constituents of water. The same 

 little atom of nitrogen may one year form a part of a 

 plant, and the next become a constituent of an animal, 

 or, with the decomposed dead animal, may form a 

 part of the soil. If the animal should fall into the 

 sea it may become food for fishes, and our atom of 

 nitrogen may form a part of a fish. That fish may 

 be eaten by a larger one, or at death may become 

 food for the whale, through the marine insect on 

 which it feeds. After the abstraction of the oil from 

 the whale, the nitrogen may, by the putrefaction of 

 his remains, be united to hydrogen, form ammonia, 

 and escape into the atmosphere. From here it may 

 be brought to the soil by rains, and enter into the 

 composition of a plant, from which, could its parts 

 speak as it grows in our garden, it could tell us a 

 wonderful tale of travels, and assure us that, after 

 wandering about in all sorts of places, it had returned 

 to us, the same little atom of nitrogen which we had 

 owned twenty years before, and which for thousands 

 of years had been continually going through its 

 changes. 



