NON-SYMBIOTIC NITROGEN FIXATION 141 



that the maximum fixation was attained where no combined nitro- 

 gen was purposely added and that on the addition of such^ fixa- 

 tion of nitrogen was diminished. 



Following Winogradski, Caron made some very interesting 

 discoveries. He found that soils under leafy crops contain greater 

 numbers of bacteria than those under grasses. He also observed 

 that the bacterial flora of soils in ' 



the spring is different from that 

 in the fall both quantitatively and 

 qualitatively. He used in vege- 

 tation experiments pure cultures 

 of the bacteria most frequently 

 encountered in natural soils. Some 

 soils were inoculated with bouillon 

 culture, whereas others received 

 only sterile bouillon. The crop 

 yields were usually in favor of the 

 inoculated plots but showed varia- 

 tions from season to seasoju- Ex- 

 ceptionally good results were ob- 

 tained with a spore-bearing bacillus which he termed Bacillus 

 ellenbachensis, 



Caron's work led to the commercial exploitation of his cul- 

 tures, one of which, *'alinit," was the subject of much study 

 and discussion. This culture was found to contain, according to 

 Severin, two closely related bacilli which he chose to designate 

 as B, ellenbachensis A. and B. These had the power to fix nitro- 

 gen to some extent. Tests with "alinit," however, have not con- 

 firmed to any great extent the claim of its exploiters. 



In 1 90 1 Beijernick's investigation led to the extremely im- 

 portant discovery of aerobic bacilli to which he gave the name 

 Axotobacter. Since that time many species of non-symbiotic 

 nitrogen-fixing organisms have been found and much learned 

 concerning their life activities, until today we recognize that the 

 power of fixing nitrogen is inherent in many bacteria, yeasts, 



Fig. 30. — Clostridium pasteurlan- 

 ium (after Winogradski). 



