SOIL BACTEEIOLOGY AS A FACTOK IX CHOP PRODUCTION. 



9 



eating or complementary action of the different groups of soil bacteria 

 which transform nitrogen compounds is more clearly expressed by a 

 diagram. Figure 1, which is self-explanatory, shows the relation of 

 bacteria to some of the most essential changes. Since the study of 

 the nitrogen-accumulating power of legumes bearing root nodules 



w:t^ 



BACTEFfiA 



CHANGE 



NimOQEN GAS INTO 



PRO TED NITROGEN 



BACTEniA or LEOUMl 



AND NON-LEGUME 



ROOT NODULES 



CHANGE 



NITROGEN GAS INTO 



PROTEID NITROGEN 



DENITRIFYING 



BACTERIA 



CHANGE 



AMMONIA TO 



NITROGEN GAS 





<^\^. 



^€o^to 



.^^ 



Fig. 1.— Diagram showing the nitrogen changes produced in the soil by the action of bacteria. The arrows 

 indicate the course of the changes which various groups of bacteria may produce in the n itrogen compounds 

 of the soil. 



deals with a defuiite and comparatively simple relation of a smgle 

 type of organism to a single type of plant, it has been possible to 

 develop these investigations upon a pure-culture basis; in other 

 words, it has been possible to isolate the nitrogen-fixing organism 

 from nodules of leguminous plants and with these cultures produce 

 77106°— Cir. 113—13 2 



