BACTERIA FIXING ATMOSPHERIC NITROGEN 127 



plants. In addition to various organic media, extracts of carrots, of 

 leaves and of seeds of leguminous plants, a number of inorganic 

 media have been suggested. Of these, several may be selected: 



1. Wood ash medium: 118 



Wood ash extract (15 grams ashes to 1 liter of tap water) . . 1000 cc. 



Sucrose 10 grams 



KH 2 P0 4 3 grams 



2. Ashby's mannite solution (p. 113J. 



3. Conn's asparaginate solution (p. 16) 



4. Glucose medium: 119 



Distilled water 1000 cc. NaCl Trace 



Glucose 20 grams FeS0 4 Trace 



KH 2 P0 4 l.Ogram MnS0 4 Trace 



MgS0 4 -7H 2 O.lgram CaCl 2 Trace 



5. Sucrose medium: 



Tap water 1000 cc. KH 2 P0 4 1.0 gram 



Sucrose 10 grams MgS0 4 0.5 gram 



6. Mannite medium: 120 



Mannite 10 grams CaC0 3 l.Ogram 



NaCl 0.2 gram Yeast water 100 cc. 



K 2 HP0 4 0.5 gram Distilled water 900 cc. 



MgSO 4 .7H 2 0.2 gram Washed agar 15 grams 



CaS0 4 -2H 2 0.1 gram 



The yeast water is prepared 121 by stirring starch-free yeast with ten times its 

 weight of tap water, steaming for 1 to 2 hours, then sterilizing and, after allowing 

 to stand 24 hours, siphoning off the clear brown liquid. 



Various legume extract and tomato extract media are also employed: A decoc- 

 tion of 100 grams material of the green plants and roots in 1000 cc. of water, to 

 which 1 per cent glucose is added and some CaC0 3 to make the reaction neutral. 1 ' 22 

 For solid media, 1.2 to 1.5 per cent of agar is used; for gelatin media, 12 per 

 cent of gelatin is used. When the reaction is adjusted by the hydrogen-ion con- 

 centration method, it should be brought to pH 6.8 to 7.5. 



118 Harrison, F. C, and Barlow, B. The nodule organism of the Leguminosae— 

 its isolation, cultivation and commercial application. Centrbl. Bakt. II, 19: 

 264-272, 426^41. 1907; Trans. Roy. Soc. Can. Ser. (2), 12: 157-237. 1907. 



119 Fred, E. B. A physiological study of the legume bacteria. Va. Agr. Exp. 

 Sta. Ann. Rpt. 1911, 145-174. 



120 Wright, W. H. The nodule bacteria of soybeans. I. Bacteriology of 

 strains. Soil Sci. 20: 95-120. 1925. 



121 Fred, E. B., Peterson, W. H., and Davenport, A. Fermentation character- 

 istics of certain pentose destroying bacteria. Jour. Biol. Chem. 42: 175. 1920. 



122 Nobbe, F., and Hiltner, L. Kunstliche Ueberfuhrung der Knollchenbak- 

 terien von Erbsen in solche von Bohnen (Phaseolus). Centrbl. Bakt. II, 6: 449- 

 457. 1900. 



