The Appropriation of Nitrogen from the Air 191 



As they became more skilled in analytical methods, 

 the chemists could not remain blind to the fact that there 

 is a constant drain on the nitrogen resources of the 

 soil. They knew that much nitrogen is removed in the 

 crops. They have learned that, in the decomposition 

 of humus, some nitrogen returns to the air in the gaseous 

 state, that another part is changed to soluble com- 

 binations and finds its way to the rivers and the sea. 

 Here then is a puzzling problem. Bare, nitrogenless 

 rock falls into fragments under the attack of the sun, 

 the winds and the rain. It crumbles more and more 

 and living things come to find lodgment in it. The 

 weathered part becomes deeper with the passing years, 

 and its vegetation grows in splendor. The rock loses 

 its identity and becomes soil, the receptacle of enor- 

 mous amounts of humus and nitrogen. In what manner 

 does the free nitrogen gas floating in the atmosphere 

 pass into the plant body, and, on the death of the latter, 

 into the soil-humus? What means are there in nature's 

 laboratory for replacing the constant losses of soil- 

 nitrogen? 



It seemed simple enough, at first, to assume that the 

 great aerial ocean furnished nitrogen directly to all 

 green plants. Such an assumption agreed well with 

 ancient traditions. The experience of many generations 

 had forced into the consciousness of the farmer the 

 belief that certain crops possessed soil-enriching quali- 

 ties. The scientific men of a hundred years ago were 

 inclined to ascribe these to the utilization of atmos- 

 pheric nitrogen. Further investigations demonstrated 

 apparently that plants cannot make use of nitrogen 



