go THE SPIRIT OF THE SOIL 



itself a slime forms round it, the nitrogen com- 

 pounds either composing the whole of the slime or 

 constituting a large portion of it. It appears to be 

 able not merely to fix atmospheric Nitrogen, but also 

 to transform nitrogenous bodies present in the soil 

 that are unsuitable for plant food into available 

 nitrogenous foodstuffs. Curiously enough, like 

 radicicola, Azotobacter very readily enters into some 

 sort of symbiotic relationships. Thus it is fre- 

 quently found living in association with green algae. 

 The association of certain other bacteria in some 

 way as yet not understood appears to increase its 

 power for fixing nitrogen. Thus, while Azotobacter 

 vinelandii is able to fix more nitrogen than Azoto- 

 bacter beyerinckii, the output of the latter can equal 

 that of the former if a certain other small bacterium 

 is present. Commenting on this remarkable fact, 

 Dr. Lipman writes : " In what manner the Azotobacter 

 are favoured by 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. 5? 



The importance of the fact in relation to bacterized 

 peat would seem to be considerable. When Azoto- 

 bacter chroococcnm is grown together with Bacillus 

 radicicola, Nitrogen fixation proceeds more satis- 

 factorily and in greater amount than if the two 

 organisms are grown separately. The character- 

 istic slime seen round Azotobacter is no longer ap- 

 parent, but long-continued experiment leaves no 

 doubt but that there is something in the nature of 



