92 THE CULTURE OF FARM CROPS. 



corps of assistants, have shown that there is much reason 

 to believe that ammonia is oxidized and changed to nitric 

 acid and in this form it is that the nitrogen enters into the 

 circulation of plants. 



To sum up the conclusions in regard to this question, of 

 such surpassing interest to farmers, which are presented by 

 a consideration of the facts known in this connection, the 

 following propositions result. 



First. That uncombined nitrogen of the atmosphere may 

 enter into the circulation to a small extent, either in its 

 natural form of a gas or in solution in water ; and this prob- 

 ably does happen. But the quantity so gained by plants 

 is very small and is wholly insufficient for their needs and 

 only a small proportion of that which vegetables actually 

 contain. 



Second. That ammonia has the power of entering into 

 plants and of yielding nitrogen to them to a very large ex- 

 tent and actually in excess of their necessities so that the 

 normal quantity of nitrogen in the product is largely in- 

 creased ; and it does appear, but is not proved, that plants 

 do derive nitrogen from this source. 



Third. That in like manner nitric acid has the power of 

 entering into plants and of yielding nitrogen to them to a 

 larger extent than they need to produce a normal product 

 and there is reason to believe that plants do derive the 

 largest portion of the nitrogen they contain from this 

 source. 



Fourth. But there is also reason to believe that ammo- 

 nia is changed to nitric acid in the soil, and perhaps in the 

 plants, and in this combination it is that nitrogen enters 

 the roots of plants and contributes to their substance. 



