516 Miss F. A. Mockeridge. Effects of Auximones on 



humified peat, evidently owing to the fact that they simply mixed the 

 materials with sand, and allowed them to remain thus for months, 

 depending solely upon the bacteria which they contained for the 

 " humifying " process. Stable manure is teeming with such organisms, 

 and conditions were ideal for their further action, but peat is practically 

 devoid of them, and they must be added under suitable conditions before 

 decomposition can take place. Hence the difference in the results obtained. 



In order to investigate further the effect of these organic substances in 

 bacterised peat, an alcoholic extract, and also the phosphotungstic and 

 silver fractions, were employed. In all cases where an alcoholic extract 

 was used, the alcohol was driven off at a low temperature by means of a fan 

 before use, and the residue taken up in distilled water. Where a water 

 extract was employed, this was sterilised in an autoclave at 135° C, in order 

 to kill off any bacteria already present. 



As already shown by Bottomley, the addition of the alcoholic extract of 

 1 grm. of bacterised peat to every 100 c.c. of culture solution resulted in a 

 marked increase in the rate of nitrogen fixation, so a comparison was made 

 of the action of the different fractions of the peat. A set of 30 flasks was 

 prepared, all containing 100 c.c. of the mannite solution, and divided into 

 five series of six flasks each. To the various series were made the additions 

 described below, and all the flasks were inoculated with 1 c.c. of a suspension 

 of a crude culture of Azotobader from soil. A similar set of 30 flasks was 

 also prepared and inoculated with a pure culture. Two flasks of each 

 series were sterilised for controls, and all were incubated for 10 days, when 

 upon analysis the results set out in Table V were obtained. 



Throughout the experiments, the beneficial effect of the fractions from 

 bacterised peat was manifested by the fact that, after about three days, 

 while the cultures in mannite alone showed still only a faint cloudiness, a 

 definite scum was already produced on the surface of those containing 

 these extracts. The figures obtained show a progressive superiority in the 

 effect of the phosphotungstic, silver, alcoholic and water extracts, and, 

 while they point to the conclusion that the active substances are not 

 separated quantitatively by the methods so far adopted, yet it is obvious 

 that all the auximone fractions have the power of increasing the rate of 

 nitrogen fixation of Azotobader. It should be noted that none of the 

 alcoholic, phosphotungstic, or silver fractions contained any trace of iron. 



The effect of the auximone fractions upon Bacillus radicicola, the nitrogen- 

 fixing organism of the leguminous nodules, was then investigated. Pure 

 cultures were obtained from the nodules of various leguminous plants, 

 notably, broad bean, sweet pea, lucerne, clover and hop trefoil, and the 



