194 GENERAL SYSTEMATIC BACTERIOLOGY 



Dicke in jungem Zustande meist als grosse Diplokokken oder als Kurzstab- 

 chen vorkommende Bakterien mit hyalinem, oft eine Vakuole fiihren dem Inhalte 

 und schleimiger Wand von sehr verschiedenen Dicke. Jiingere Zustande mehr 

 oder weniger beweglich vermittels einzelner polarer oder in polaren vier — bis 

 zehnzahligen Biindeln angeordneten, kurzen Cilien, welche umgefahr so lang sind, 

 wie die Bakterien selbst. Sporen fehlen, das heisst, wachstumfahig in Nahrlosun- 

 gen mit geeigneten Kohlenstoff quellen, welche sehr arm sind an Stickstoffver- 

 bindungen assimiliert den atmosphaerischen Stickstoff, und ist dadurch in Bezug 

 auf die iibrige Mikrobenwelt konkurrenzfahig Optimum temperature 28°. 



The type species named was Azotobacter chroococcum. 



Beijerinck and van Delden (1902, p, 3) again described the genus. 

 The genus was rejected by Erwin F. Smith (1915). It was accepted by 

 Stockhausen (1907, p. 88), The genus is quite generally recognized 

 by writers on agricultural bacteriology. Orla-Jensen (1909, p. 328) 

 changes the name of this genus to Azotomonas and places it in his family 

 Oxydobacteriaceae . 



Lohnis and Hanzawa (1914, p. 1) claim to have demonstrated that 

 the organisms of this genus may at certain stages in their life his- 

 tory produce endospores. They conclude that Azotobacter is therefore 

 an invalid synonym of Bacillus. The type species is renamed Bacilhis 

 azotobacter. It may be noted that even though the genus should be 

 Bacillus, the species should be designated B. chroococcus in accordance 

 with the botanical rules. 



Winslow et al. (Committee 1917, p. 552) and Bergey et al. (1923, p. 38) 

 accept the genus with the following diagnosis : 



Relatively large rods, or even cocci, sometimes almost yeast-like in appear- 

 ance, dependent primarily for growth energy upon the oxidation of carbohydrates. 

 Motile or non-motile; when motile, with tuft of polar flagella. Obligate aerobes 

 usually growing in a film upon the surface of the culture medium. Capable of 

 fixing atmospheric nitrogen when grown in solutions containing carbohydrates 

 and deficient in combined nitrogen. The best-known free-living nitrogen-fixing 

 bacteria of the soil. 



The same description is used by the Committee in 1920 (p. 203). 

 Buchanan (1918, p. 46) describes the genus as follows: 



Relatively large rods, or even cocci, sometimes almost yeast-like in appear- 

 ance, dependent primarily for growth energy upon the oxidation of carbohydrates ; 

 obligate aerobes, usually growing in a film upon the surface of the culture media. 

 Capable of fixing atmospheric nitrogen in considerable amounts when grown in 

 solutions deficient in combined nitrogen. Motile or non-motile, if the latter, with 

 polar flagella. 



