STUDIES ON GROWTH CYCLE OF AZOTOBACTER 327 



fluorescens, Bad. pneumoniae, Sar. flava, Strep, lactis, Lactobacil- 

 lus bulgaricus and others, they use the azotobacter life cycle more 

 than any other to demonstrate the truth of their conclusions. 

 They give a diagrammatic representation of the life cycle of 

 azotobacter with drawings of the many types of cell structures 

 observed and suggest how these forms may be related to one 

 another. A number of photomicrographs are also presented to 

 the same end in the article. 



Though the writer has not so far observed the complexity 

 of the life cycle in any other species of bacteria than the azoto- 

 bacter, he has observed it in this species, to a greater or less 

 extent, as pointed out in the articles previously referred to, 

 published in 1913 and 1914. He finds, however, that while he 

 agrees with some, he cannot agree with all the conclusions arrived 

 at by Lohnis and Smith with regard to azotobacter. 



SPORE FORMATION BY AZOTOBACTER? 



In the first place Lohnis and Smith refer to azotobacter as a 

 heat-resistant endospore-forming bacillus, and point out that 

 another investigator, Mulvania, reports the presence of heat- 

 resisting spores in azotobacter. Further, they state that while 

 other investigators failed to report the finding of resistant spores 

 in azotobacter, "They undoubtedly would have found them by 

 a more thorough search." Lohnis and Smith observed two 

 types of spore-forming rods in the complex cycle of the azoto- 

 bacter, one a small rod and the other a large rod. They also 

 observed non-spore-forming rods both small and large, but 

 neither of these ever developed directly into spore-formers, 

 although the small spore-forming rod sometimes developed into 

 the large spore-forming rod. 



They imply that the faculty of heat-resistant endospore pro- 

 duction is not constant in the azotobacter as only about 50 per 

 cent of their cultures possessed it and most of these had developed 

 it only after being kept in the laboratory for a number of years. 



When the writer was isolating from the soil the varieties 

 of azotobacter which he studied, he frequently found spore- 

 forming rods, both large and small, cropping up in his cultures 



