BACTERIA FIXING ATMOSPHERIC NITROGEN 117 



Azotobacter was found in most Javan soils, 60 in all soils in India 61 in a 

 half of Polish soils 62 and in about 33 per cent of the cultivated soils in 

 Japan. 63 The wide distribution of Azotobacter in Russian soils, in 

 Utah soils 64 and in Danish soils 65 has also been pointed out. How- 

 ever, Azotobacter is almost completely absent in Finnish soils, even 

 those that are well buffered and supplied with CaC0 3 . 66 



Azotobacter derived from different localities may vary greatly in the 

 amounts of nitrogen fixed. In humid regions the nitrogen-fixing or- 

 ganisms are confined to the upper few inches of soil. 67 However, in 

 arid regions, they may be quite active to a depth of 3 to 4 feet. Azoto- 

 bacter occurs more frequently in cultivated than in virgin soils. The 

 number of Azotobacter in the soil is highest in spring and fall of year 

 and lowest in summer and winter. According to Beijerinck, the num- 

 ber of Azotobacter in the soil runs parallel with soil fertility. It is 

 interesting to note that Azotobacter is among the first organisms to 

 develop in a newly formed soil, as in the case of Vesuvian soils. 68 



Lohnis and Smith recognized only two species of Azotobacter isolated 

 so far: A. cliroococcum and A. agile Beij. (Syn. A. vinelandii J. G. 

 Lipman). A. beijerinckii Lipman was looked upon as a variety of A. 

 chroococcum and A . vitreum Lohnis as a variety of A . agile. 



Morphology and life cycle of Azotobacter. The form and size of 

 Azotobacter cells depend upon the composition of the medium and 

 conditions of cultivation. Increased aeration brings about a lengthen- 

 ing of the forms and greater motility. In the presence of organic 

 colloidal substances, especially those containing nitrogen, as well as 

 aluminum salts, the cells remain in a young condition for a long time; 



60 Groenewege, J. Occurrence of Azotobacter in tropical soils. Arch. Sui- 

 kinderind. 21: 790-793. 1913. 



61 Hutchinson, C. M. Soil bacteriology. Rpt. Agr. Res. Inst. Pusa. 1911-12, 

 85-90; Azotobacter and nitrogen fixation in India soils. Mem. India Agr. Exp. 

 Sta. Bact. Ser. 1: 98-112. 1915. 



62 Ziemiecka, J. Presence de l'azotobacter dans les sols polonais. Rocznikow 

 Nauk Rolniczych. 10: 1-78. 1923. 



63 Yamagata, U., and Itano, A. Physiological study of Azotobacter chroococ- 

 cum, beijerinckii and vinelandii types. Jour. Bact. 8: 521-531. 1923. 



64 Greaves, J. E. Azofication. Soil Sci. 6: 163-217. 1918. 



66 Weis, F., and Bornebusch, C. H. On the presence of Azotobacter in Danish 

 woods. Det. Forstlige Forsogs. Danmark, 4: 319-331. 1914. 



66 Brenner, W. Azotobacter in finnlandischen Boden. Geolog. Konn. Fin- 

 land. Agr. Geol. Meddl.20: 1924. 



67 Ashby, 1907 (p. 113). 



68 Riccardo, 1923 (p. 110). 



