252 AZOFICATION . 



van Tieghem. Since this, however, there has been described at 

 least one aerobic clostridium. Moreover, Omelianski considers 

 that the Clostridium pasteurianum, isolated from the Russian soils, 

 is clearly a morphologically distinct race. An idea of the activity 

 of some organisms in fixing nitrogen may be obtained from the fol- 

 lowing results reported by Lohnis. In every 100 c.c. of 1 per cent, 

 mannite, or grape sugar soil extract, there was fixed, in the course 

 of three weeks, nitrogen as follows: 



Mg. 



Bact. chrysogloea . . ' 1.4 



Bact. tartaricus 0.3 



Bact. lipsiense 0.2 



C. B. Lipman tested 18 organisms, including yeasts, pseudo- 

 yeasts, and molds, nearly all of which showed a more or less pro- 

 nounced power of fixing atmospheric nitrogen. 



Pringsheim has isolated from ordinary garden soil certain thermo- 

 philic organisms which fix from 3 to 6 mgm. of nitrogen per gram of 

 dextrose when incubated at 61 C. in a Winogradsky's solution to 

 which a little soil extract was added. Duggar and Davis have 

 recently investigated the subject of the fixation of nitrogen by the 

 filamentous fungi, Aspergillus niger, Macrosporium commune, Peni- 

 cillium digitatum, Pexpansum, Glomerella, Gossypii, and Phoma 

 beta, and of these only the last-named was definitely proved to be 

 able to fix nitrogen. It is thus seen that the power of fixing nitrogen 

 is a characteristic possessed by many microorganisms, in contradic- 

 tion to the supposition of Winogradsky that this^power is limited 

 to a particular, or, at most, a few species. This is especially empha- 

 sized by the recent work of Emerson who examined soil which 

 contained 2,400,000 organisms per gram which would develop on 

 nitrogen-free media. Of these, 97 per cent, possessed the power 

 of fixing nitrogen; they constituted at least four distinct groups. 

 Nevertheless, the most important group yet discovered is the 

 Azotobacter, and it is with these mainly that this chapter deals. 



Distribution. The nitrogen-fixing organisms are widely distributed, 

 occurring in most soils. Lipman and Burgess, who studied the nitro- 

 gen-fixing flora, especially those of the Azotobacter group, of 46 soils 

 from Egypt, India, Japan, China, Syria, the Hawaiian Islands, 

 Guatemala, Costa Rica, Spain, Italy, Russia, Mexico, Asia Minor, 

 Canada, Unalaska, Samoa, Australia, Tahiti, Belgium, Queensland, 

 and the Galapagos Islands, found every soil possessed the power of 

 fixing nitrogen in mannite solution. About one-third of the soils 

 contained Azotobacter', frequently the same soil showed the presence 

 of two or three different species of Azotobacter. A. chroococcum, 

 however, was the most prominent. It was also found most widely 

 distributed in the various soils. Groenewege found Azotobacter in all 

 but one of a series of Java soils. 



Several hundred Utah soils have been examined and all found to 

 fix nitrogen, many of them without the addition of carbohydrates. 



