262 AZOFICATION 



starch, but there was practically no increase when straw, filter 

 paper or buckwheat was applied. Yet Stoklasa showed that the 

 decomposition products of these substances acted as a valuable 

 source of energy to the Azotobacter, and Stranak considered that the 

 pentosans of the soil are of the greatest importance in the assimila- 

 tion of nitrogen by soil bacteria. 



A fair idea of the great variety and relative efficiency of substances 

 which may serve as a source of energy to the azofiers may be obtained 

 from the work of Lohnis and Pillai. They inoculated a nutritive 

 solution with 10 gm. of soil and after ten days determined the gain 

 in nitrogen. 



Nitrogen fixed 



Substance added. afterlO days 



mgm. 



Mannite 9.40 



Xylose 9.54 



Lactose 9.12 



Levulose 8.52 



Inulin 7.72 



Galactose 7.86 



Maltose 7.44 



Arabinose . . . . 7.62 



Dextrin 7.18 



Sucrose 8.60 



Dextrose 4.62 



Starch 3.36 



Sodium tartrate 2.82 



Glycerin . 1.68 



Sodium succinate . . . . . 2.96 



Calcium lactate . . . 2.49 



Sodium citrate . . . . . . . . 1.42 



Sodium propionate 1.10 



Potassium oxalate .0.12 



Calcium butyrate 0.02 



Humus . . . -0.96 



Other workers have noted larger gains of nitrogen than those 

 noted by Lohnis and Pillai, but they can readily be attributed to the 

 time of incubation in this case, ten days being far too short for the 

 complete utilization of the carbonaceous substance applied; the 

 species of nitrogen-fixers which are bringing about the change; and 

 whether pure or mixed cultures are used. The order of effectiveness 

 noted above, however, is that recognized by most workers. Brown 

 and Allison, however, do report results in which greater fixation 

 was obtained with dextrose than with mannite. But in this case, 

 calcium or sodium carbonate seems to be even more necessary than 

 it is with the mannite. Moreover, some species utilize one carbo- 

 hydrate most effectively and another species a different one. To 

 this list may be added malate, gum tragacanth, ethylene glycol, 

 methyl, ethyl, and propyl alcohols, lactic, malic, succinic and gly- 

 collic acids. Fatty acids are readily utilized, the amount of nitrogen 

 fixed being greater with the increased molecular weight, from 1.47 

 mgm. with formic acid, to 6.08 mgm. with butyric acid. Most of the 



