Chemical Processes in Plants. 327 



cultivated thereon : Bac. ramosas, nitrosomonas, and 

 nitrobacter. With the first-named alone, only ammonium 

 salts were produced from the bouillon ; and with the two 

 last-named alone, the bouillon remained unchanged. With 

 the first two the nitrification was carried only to the 

 nitrite stage. To produce nitrates from the bouillon the 

 co-operation of all three classes of bacteria was necessary, 

 and the nitrification took place in three stages. The 

 various other experiments indicate that plants make use 

 of their nitrogen when it is offered in the form of 

 simpler inorganic compounds, and Chili saltpetre (sodium 

 nitrate) has for a long time been regarded as the source 

 par excellence of the nitrogen for crops. Water-culture 

 experiments show, at any rate, that nitrates can be used as 

 the sole source of nitrogen for the building up of complex 

 organic nitrogen compounds in plants, which in this respect 

 act in marked contrast to animals which utilize the complex 

 proteins as their chief source of nitrogenous food. 



Certain lupines can, furthermore, indirectly utilize the 

 nitrogen of the air for building up complex proteins. It 

 was first observed by Lawes and Gilbert that leguminosae 

 (such as peas and beans) could grow continually in a soil to 

 which no nitrogenous manure had been added without 

 producing exhaustion of nitrogen. In fact, more nitrogen 

 could be taken from the soil than had been added. The 

 results of these experiments were in direct contradiction to 

 those obtained by Boussingault, who found that leguminosae 

 would not grow in a soil which had not been supplied with 

 nitrogenous material, and who drew from his results the 

 conclusion that plants were unable to utilize the nitrogen 

 of the air. The discrepancy between the observations of 

 Lawes and Gilbert on the one hand, and of Boussingault 

 on the other hand, was finally explained by Hellriegel 

 and Wilfarth. The capacity of producing nitrogenous 



