THE FAMILIES AND GENERA OF THE BACTERIA 203 



motile, with tuft of polar flagella. Obligate aerobes usually 

 growing in a film upon the surface of the culture medium. Cap- 

 able of fixing atmospheric nitrogen when grown in solutions con- 

 taining carbohydrates and deficient in combined nitrogen. 

 The type species is Azotobacter chroococcum Beijerinck. 



Genus 8. Rhizobium Frank, 1889, p. 338. 



Synonyms: Phytomyxa Schroeter 1886; Cladochytrium Vuillemin 1888; 

 Rhizobacterium Kirchner 1895; Pseudorhizobium Hartleb 1900; Rhizo- 

 monas Jensen 1909. 



Comment. Phytomyxa Schroeter has priority over Rhizo- 

 bium, but because of the confusion which would arise from the 

 substitution of the older correct name for the better known term 

 Rhizobium, the committee recommends the adoption of the latter. 



Minute rods, motile when young. Involution forms abundant 

 and characteristic when grown under suitable conditions. Ob- 

 ligate aerobes, capable of fixing atmospheric nitrogen when grown 

 in the presence of carbohydrates in the absence of compounds of 

 nitrogen. Produce nodules upon the roots of leguminous plants. 



The type species is Rhizobium leguminosarum Frank. 



Family II. Pseudomonadaceae, Committee 1917b, p. 555 



Rod-shaped, short, usually motile by means of polar flagella 

 or rarely non-motile. Aerobic and facultative. Frequently gela- 

 tin liquefiers and active ammonifiers. No endospores. Gram 

 stain variable, though usually negative. Fermentation of car- 

 bohydrates as a rule not active. Frequently produce a water- 

 soluble pigment which diffuses through the medium as green, 

 blue, purple, brown, etc. In some cases a non-diffusible yellow 

 pigment is formed. Many yellow species are plant parasites. 



Genus 1. Pseudomonas Migula 1894, p. 237, emended 



Synonyms: Bacterium Ehrenberg emended Cohn 1872; Bactrillum 

 Fischer 1895; Arthrobactrinium Fischer 1895; Arthrobactrillum Fischer 

 1895; Eupseudomonas Migula 1895; Bactrinius Kendall 1902; Bactril- 



