AGRICULTURE AND RURAL ECONOMY. 363 



with the words: "And now, to summarize in a few words 

 the results of this whole discussion, I think the balance of 

 the evidence points to the conclusion that the answer to the 

 question, What are the sources of the nitrogen of vegetation 

 in general, and of agricultural productions in particular? is 

 more likely to be found in the relations of the atmosphere 

 and of the plant to the soil than in those of the atmosphere 

 to the plant itself." 



On the whole, the evidence is decidedly against the theory 

 so stoutly maintained by some, particularly Ville, that plants 

 obtain considerable, some a large share, of their nitrogen by 

 their leaves from the air. 



Best Forms of Nitrogen for Plant-Food. 



The important question as to the form of nitrogen most 

 suitable for the nutrition of plants has been studied by Leh- 

 mann, who has lately experimented with buckwheat, maize, 

 and tobacco, supplying nitrogen in some cases in the form 

 of nitrates, and in others in the form of ammonia salts. He 

 concludes that some plants require ammonia in their first 

 period of vegetation, and nitric acid in the second, but that 

 ammonia may, by oxidation in the soil, produce the nitric 

 acid needed. 



Hasselbarth has studied the assimilation of nitrogen by 

 barley. The whole of the nitrogen was absorbed, and the 

 total yield of dry substance the same, when the nitrogen was 

 supplied as calcium nitrate or as ammonium nitrate in soil 

 free from marl. In marled soil the nitrogen was wholly ab- 

 sorbed when supplied as ammonium sulphate or chloride. 

 When the latter salts were applied to unmarled soils, only 

 one half of the total nitrogen was absorbed. The worst re- 

 sults were obtained by using acid ammonium phosphate: in 

 marled soil only three fifths and in unmarled soil only one 

 seventh of the nitrogen was absorbed, the yield being corre- 

 spondingly small. It appears from these experiments as 

 though barley could absorb the nitrogen only when present 

 as a nitrate, or under conditions that permit of ready trans- 

 formation to a nitrate (Chem. GentralMatt, 1876, 821). 



It is worthy of note here that in the experiments of Lawes 

 and Gilbert on grass land, nitrogen in the form of nitrate of 

 soda, which finds its way into the deeper layers of the soil 



