FROM THE AIR BY THE LEGUMINOS^ I5 



subsequently planting this same soil with clover. In the 

 first period there was no increase in nitrogen, and in the 

 second there was a considerable surplus. 



Although the results obtained by these various scientists 

 are distinctly similar, their explanations differ. Dietzell takes 

 no account of free atmospheric nitrogen, and believes that 

 phosphoric acid in solution favours the association in the soil 

 of nitrogen with other substances. 



Atwater and Joulie stated the absorption of nitrogen by 

 the Leguminosaj as a fact, but assigned no reason. Franck 

 believed that there exist in the soil two mechanical forces : 

 one tending to release nitrogen from its compounds, the other 

 endeavouring to bring about these combinations. This force 

 is assisted by the presence of plants living in the soil. Wolf's 

 theorv was that the humidity in the soil absorbs ammonia, 

 and thus occasions the surplus of nitrogen ; but he was 

 astonished that this attracting force favoured the absorption 

 of the nitrogenous element only in the Leguminosse. 



Strecker refused to admit that the LeguminoSce had the 

 power of absorbing additional nitrogen, and considered 

 that it was only a question of amount. 



Inquiry into External Causes. 



In 1875 M. Berthelot assigned to certain non-nitrogenous 

 organic substances, such as, for instance, cellulose, benzine, 

 turpentine, &c., the property of fixing atmospheric nitrogen 

 when submitted to an electric current. 



In 1885, that is to say, ten years later, Berthelot attri- 

 buted to clay soils, as well as to the micro-organisms they 

 contain, an action on the fixation of nitrogen. In 1886, in 

 a second memoir, he investigated the nature and proportion 

 of the organic matter present in these soils, matter without 

 which the living micro-organisms, with their capacitv for 

 fixing atmospheric nitrogen, are unable to exist. 



Later on, Berthelot continued his researches on vegetable 

 soils with the aid of plants, and gave his conclusions as 



