104 SOILS AND FERTILIZERS 



plants had well-formed swellings or nodules, while 

 those that were watered with distilled water alone had 

 none. The loam leachings contained only a trace of 

 nitrogen. 42 



122. 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 leachings from 

 an old lupine field. 



Watered with distilled water. Watered with soil leachings. 



Dry matter. Nitrogen. Dry matter. Nitrogen. 



Grams. Grams. Grams. Grams. 



0.919 0.015 44-72 1-099 



0.800 0.014 45-6i i .153 



0.921 0.013 4448 I-I95 



i. 021 0.013 42.45 T -337 



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. 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. 



123. Composition of Root Nodules. The root 

 nodules referred to, are particularly rich in nitrogen. 

 In one experiment, the light-colored and active ones 

 contained 5.55 per cent., while the dark-colored and 

 older ones contained 3.21 per cent. The entire 

 nodules of the root, both active and inactive, con- 



