46 R. E. BUCHANAN 



Genus 2. Rhizobium Frank, 1889, p. 338 



Synonyms : 



Cladochytrium Vuillemin, 1888, p. 121 

 Phytomyxa Schroeter, 1886, p. 134 

 Schinzia Denstatt, 1818, in part 

 Rhizohacterium Kirchner, 1895, p. 213 

 Pseudorhizobium Hartleb, 1900, p. 887 

 Rhizomonas Jensen, 1909a, p. 334 



Rod-shaped cells, motile when young by means of polar flagella, 

 obligate aerobes, fixing atmospheric nitrogen when grown in a ni- 

 trogen-free medium containing suitable carbohydrates, involution 

 forms abundant and characteristic, usually growing in the nodules 

 of the roots of leguminous plants. 



The type species is Rhizobium leguminosarum Frank. 



The name of this genus has been a source of confusion. The 

 organism of leguminous nodules was placed in the mold genus 

 Schinzia by Frank as Schinzia leguminosarum. Schroeter (1886, 

 p. 134) concluded the organism to be one of the slime molds 

 and created the genus Phytomyxa, including it in the order 

 Phyto7nyxini among the Myxomycetes. He based his conclusions 

 as to the position of this organism among the slime molds upon 

 the work of Prilleaux (1879, p. 98). Beijerinck (1888, p. 758) 

 named the organism Bacillus radicicola. Frank (1889, p. 338) 

 renamed the organism Rhizobium leguminosarum. The fact that 

 Schroeter included this genus incorrectly among the slime molds 

 does not invalidate the name. The Committee on Classifica- 

 tion of Bacteria, of the Society of American Bacteriologists, 

 however, has recommended the use of the generic name Rhizo- 

 bium as better known and probably resulting in less confusion 

 than the use of Phytomyxa. 



Genus 3. Azotobacter Beijerinck, 1901d, p. 561 



Relatively large rods, or even cocci, sometimes almost yeast- 

 like in appearance, dependent primarily for growth energy upon 

 the oxidation of carbohydrates; obligate aerobes, usually growing 



