TRANSFORMATIONS OF CARBON AND NITROGEN. 97 



a rod (Nitrosobacter) and the other a coccus (Nitrosococcus), 

 (Fig. 16, A.) 



Xitric bacteria, called Xitrobactcr. This is the second species 

 which completes the nitrification, changing the nitrites into 

 nitrates. (Fig. 1 6, B and C.) 



All of these species of bacteria are very widely distributed 

 in nature and have been isolated from soils of widely separated 

 localities. Apparently the nitrobac- 

 teria are almost universally distrib- 

 uted in soils all over the world. * 

 The bacteria isolated from the dif- 

 ferent soils show a certain amount 

 of variation among themselves, but *jlf % 

 they show such decided likenesses V 

 in their general characters that they 

 can all be properly classed together 

 as nitrobacteria and divided into, the Nitrifying bacteria : A, 



B and C, nitric bacteria. 



few species above defined. Both 



types are commonly found in the soil, so that the nitrification, 

 if it occurs, will be complete, the one raising the ammonia to 

 nitrites and the other completing the oxidation into nitrates. 

 Their importance in the soil can hardly be overestimated, since 

 they complete the final transformation of nitrogen compounds 

 into the form most available for plants, and thus unlock much 

 of the soil nitrogen from its useless combinations. 



A graphic representation of these nitrogen transformations 

 may serve to bring this subject more clearly before the mind. 

 In Fig. 17 is represented the nitrogen cycle of transformation. 

 Beginning at the bottom of the circle, in the form of nitrates, 

 the nitrogen may be traced around the circle in its transforma- 

 tions through various organisms, until such parts of it as do 

 not fly off from the circle entirely get back to their starting 

 point. 



Nitrifying Bacteria in the Soil. What is the actual relation 



