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



as such. In order to investigate farther this property a fractionation of 

 the bacterised peat was made according to the methods already described by 

 Bottomley,* and the decomposed phosphotungstic-acid fraction obtained. 

 Four portions, each consisting of 40 oz. of soil from Chelsea Physic Garden, 

 were weighed out, and to each of two of them was added, in solution in 

 distilled water, the phosphotungstic fraction of that weight of bacterised 

 peat which, if mixed with the soil, would give a proportion of one part of 

 peat in ten of soil by bulk ; the other two served as controls. The four soils 

 were sampled at once for their nitrogen content, and were then placed in 

 loosely corked glass bottles on top of the incubator as before, for about seven 

 weeks, moisture being added when necessary, and the bottles being shaken 

 daily. Samples analysed twice during that period gave the following 

 results : — 



Table III. 





Original 

 nitrogen 

 content (mgrin. 

 per 100 grm. — 

 mean of three 

 determinations). 



Nitrogen 

 content after 

 28 days (mean 



of three 

 determinations). 



Nitrogen 

 content after 

 52 days (mean 



of three 

 determinations) . 



Gain in 

 28 days. 



Gain in 

 52 days. 



1. 



Soil alone 



312 



321 



333 



9 



21 



2. 



Soil + phosphotungstic 



316 



322 



335 



6 



19 



3. 



314 



• 333 



373 



19 



59 





fraction 













4. 





317 



337 



380 



20 



53 



The figures here given show that the addition of even the phospho- 

 tungstic fraction to the soil results in an increase in nitrogen fixation, 

 although it is not to be expected that this fraction would be as effective as 

 the bacterised peat itself. This substance certainly contains neither 

 organisms nor soluble humus as such, nor can it have any effect on the 

 physical condition of the soil. As a result of these investigations, a com- 

 parison was made between the effect of humus from raw peat and that 

 from bacterised peat and its various fractions, upon the nitrogen-fixing 

 organisms in liquid culture. 



It has already been shown by Krzemieniewskij- that the addition of natural 

 humus to the culture medium in whicli Azotobacter chrooeoccum is growing 

 results in a greatly increased nitrogen fixation, so a solution of this natural 

 humus was prepared by treating some of the raw peat used in the prepara- 

 tion of the bacterised peat with just sufficient sodium carbonate solution to 



* Bottomley, W. B., 'Roy. Soc. Proc.,' B, vol. 88, pp. 237-247 (1914). 



t Krzemieriiewski, 'Bull. Acad. Sci. Cracovie,' No. 9, pp. 929-1050 (1908). 



