RECLAIMING LOST N1TKOGKN. I 51 



in one or another legume, and having become especially 

 adapted to growth in the pea does not so readily develop in 

 the root of the bean or clover ; but, allowed to develop in the 

 soil in which the latter plants are growing, it will adapt itself 

 as well to the new plant as to the old. In other words, the 

 present condition of experiments indicates that there is only 

 one of these species of tubercle bacteria, and that this species 

 assumes different physiological characters under the influence 

 of the different conditions in which it grow r s. It may adapt 

 itself especially for growth in one leguminous plant and conse- 

 quently lose its ability to develop well in others ; but, if a 

 new legume is planted in the same soil, a slow change of 

 physiological characters takes place, and the soil organism 

 becomes in time adapted to the new leguminous plant. This 

 conclusion is clearly in complete harmony with the fact that the 

 soil may at any time contain the organisms w r hich will support 

 one species of legume luxuriantly, while another species will 

 have only a scanty growth. 



IMPORTANCE OF THE LEGUMINOUS CROPS TO AGRICULTURE. 



Although we may not know as yet exactly how this combi- 

 nation of legume and bacteria works to fix free nitrogen, the 

 fact is none the less cogent. It becomes a matter of great 

 significance to agriculture to determine the best practical 

 method of making use of this power. Evidently there is here 

 a great opportunity for the fixation of nitrogen without pur- 

 chasing it and, if properly used, it w r ould seem that we have 

 here the factor needed for making possible a cultivation of the 

 soil without exhausting its nitrogen. Virgin soil has all its 

 factors of- nitrogen loss and gain nearly balanced ; cultivated 

 soils have a balance on debit side. If we can discover a prac- 

 tical method of applying these factors of nitrogen assimilation, 

 one of the great agricultural problems will be solved. Up to 

 the present time the matter has not been brought to a condi- 



