TRANSFORMATIONS OF CARBON AND NITROGEN. 1 03 



building up a certain amount of organic material which might 

 subsequently serve as nourishment for higher plants. They 

 may thus be a not unimportant factor in the disintegration of 

 rocks, and a more important factor in the beginning of the dep- 

 osition of foods in the soil upon which vegetation may subse- 

 quently depend. They would thus seem to be an even more 

 fundamental link between the organic and the mineral world 

 than the green plants, since they are able to make use of even 

 simpler forms of nitrogen. Ammonia and nitrites are of little 

 use to ordinary plants, but they furnish these bacteria with 

 their nitrogen and energy. Hence w r e must look upon these 

 nitrobacteria as of great significance in the formation of soils, 

 and in their extraordinary power of living without organic food 

 or sunlight, they are in the sharpest contrast to all other living t , 

 organisms known at the present time. 



RELATION OF DENITRIFICATION AND NITRIFICATION IN THE 



SOIL. 



These peculiar properties of the nitrifying bacteria enable us 

 to understand, in part at least, their relation to the denitrifica- 

 tion process in the soil. The building of nitrates will not take 

 place in the soil so long as there is any considerable amount 

 of organic material or any considerable amount of free ammonia 

 present If there is much organic material rapidly decompos- 

 ing so as to produce ammonia, this will completely check the 

 formation of nitrates, for these nitrifying bacteria will not grow 

 in the presence of either organic material or ammonia. It is 

 not until after decomposition has been completed and prac- 

 tically all the organic compounds used up that the nitrifying 

 germs can begin to act. The denitrifying bacteria cease to 

 grow after they have used up all the organic material which 

 nourishes them, and, therefore, even if nitrates are subsequently 

 produced they will not be reduced by the nitrifying organisms 



