p #s3 





148 BACTERIA AND SOIL FERTILITY 



wonderful advancements of the past decade will seem as little 

 beside it. 



Properties of Azotobacter.— In size and shape the A%oto- 



hacter are more like the yeasts than bacteria. Thev are eo-o-- 

 11*1 " 



shaped with a marked tendency to form agglomerations and often 



occur as involution forms. They are accompanied by small rod- 

 shaped organisms with which they 

 C^ **^%, probably live in a form of svm- 



*^2 * ' ^#% *^ biosis, the full significance of 



^*^ #^^ #t which IS not well understood. It 



f %A may be that they help the Jzoto- 



|fj| bacter digest the more resistant 



#,£^ plant tissue and use up much of 



* the fixed nitrogen, and hence the 



Azotobacter are stimulated to 



greater activity. 



When grown in the laboratory 

 "'^'*^ they produce very interesting: 



Fig. 31. — Azotobacter cells. . •' ^ 



(After LohnJs.) pigments. These vary in color 



^^^ from brown to black of A, 



chroococcum to a yellow or orange of the A, vinelandii. The 

 power to produce this pigment at times is lost, but they continue 

 just the same to fix nitrogen. Probably the pigment is just a 

 curious by-product which has no importance. The intensity of 

 the pigment varies with the medium on which the organism is 

 grown. It is intensified by the presence of nitrates. 



Soil Inoculation. — High hope was entertained that the nitro- 

 gen problem in agriculture had been solved when Caron an- 

 nounced that he had prepared a culture of bacteria which would 

 enable non-leguminous plants to utilize free atmospheric nitro- 

 gen, provided certain precautions were observed. Many of the 

 results which he reported on pot experiments were clearly in favor 

 of the inoculated soil. Stoklasa was one of the first to study in 

 detail the commercial preparation "alinit" which was placed on 

 the market as a result of Caron's work. His findings were fully 

 as favorable as Caron's, but the work of others soon demonstrated 



