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SOILS AND FERTILIZERS 



133. Experiments of Wilfarth. - - Experiments by 

 Wilfarth give more exact data regarding the amount 

 of nitrogen taken from the air. Two plots of lupines 

 were grown ; one was watered with distilled water, while 

 the other received in addition a small amount of leach- 

 ings from an old lupine field. 



These experiments have been verified by many other 

 investigators until the fact has been established that 

 leguminous plants may, through the agency of micro- 

 organisms, make use of the free nitrogen of the air. 

 When legumes were grown in closed vessels and the air 

 was analyzed, it was found that there was a loss of 

 nitrogen from the air proportional to that gained by the 

 plants. 



The work of Hellriegel was not accidental, but the 

 result of careful and systematic investigation. As early 

 as 1863 he observed that clover would develop along the 

 roadway in sand in which there was scarcely a trace of 

 combined nitrogen. 



