170 AMMONIA. 



present in highly-manured soils, hydrogen exists to 

 the amount of nearly one-fourth of its weight. On 

 the extent, therefore, to which this gaseous com- 

 pound gains admission by the roots into the plant 

 will depend the supply of hydrogen which they are 

 capable of drawing from this source. Had we sat- 

 isfactory evidence of the absorption of this gas by 

 the roots or leaves of plants in any quantity, we 

 should find no difficulty in admitting that plants 

 might from this source easily obtain a considerable 

 supply of both carbon and hydrogen. We could 

 also explain how, that is, by what chemical changes, 

 it is capable of being • so appropriated ; but the 

 extent to which it really acts as food for vegetables 

 is entirely unknown. 



"Ammonia is another compound containing much 

 hydrogen (one equivalent of nitrogen to three of 

 hydrogen), which exercises a manifest influence on 

 the growth of plants. If this substance enters into 

 their circulation in any sensible quantity, — if, as 

 some maintain, it be not only universally diffused 

 throughout nature, but is constantly affecting and 

 influencing at all times the functions of vegetation, 

 — there can be no doubt that the hydrogen it con- 

 tains must, to an equal extent, be concerned in the 

 production of the various organic substances which 

 are formed or elaborated by the agency of vegetable 

 life. The quantity of ammonia which actually 

 enters the circulation of plants in a state of nature 



