202 



Bacteria in Relation to Country Life 



not nitrogen-fixing organisms. The writer demonstrated 

 that the increased power thus lent to the nitrogen- 

 fixing bacteria may be very considerable, and that the 

 several azotobacter species show differences in this 



respect. For in- 

 stance, it was 

 found by the 

 writer that Azoto- 

 bacter Vinelandii 

 can fix much larger 

 quantities of nitro- 

 gen than Azoto- 

 bacter Beyerinckii 

 When, however, 

 the latter is devel- 

 oping in the pres- 

 ence of a certain 

 small bacillus, its 

 output of com- 

 bined nitrogen 

 may equal that of 

 Azotobacter Vinelandii. We are, therefore, confronted 

 here by a relation which may be designated as sym- 

 biosis. It may be assumed safely that the organisms 

 accompanying the azotobacter are enabled to develop 

 because of the nitrogen compounds elaborated by 

 the former. In what manner the azotobacter are favored 

 by the growth of the accompanying organisms is not 

 known. It is likely, however, that the latter use up much 

 of the nitrogen fixed by the azotobacter and that these 

 are, therefore, compelled to increase their activities. 



Fig. 32. B .30; X 1,000. A small bacillus 

 which cannot by itself hx atmospheric nitro- 

 gen but stimulates the activities of nitrogen- 

 fixing organisms. 



