104 



Prof. W. B. Bottomley. 



which, if incorporated with the soil, would have given a mixture of 10 parts 

 of soil to one part of peat by volume, the proportion used in the preliminary 

 experiments. The weight of solid matter thus introduced amounted to 

 - 051 grm. After small portions of each had been weighed out for analysis, the 

 two samples of soil were put into wide-mouthed glass bottles, loosely corked, 

 and kept at laboratory temperature for some weeks, the bottles being well 

 shaken daily to ensure aeration, and distilled water added when necessary, to 

 maintain a uniform moisture-content. Small samples were taken from time 

 to time, and their nitrate-content determined by the phenol-sulphonic acid 

 method, with the following results : — 



Table II. 





Nitric nitrogen in parts per million on — 





April 6. 



April 20. 



April 30. 



May 12. 



May 26. 



" Soil 



11 



78 



95 



228 



316 





14 



153 



305 



471 



662 



These results suggested that liquid cultures of the nitrifying organisms 

 might furnish a test for plant auximones. A culture was therefore 

 obtained by placing 10 grm. of garden soil in a flask containing 100 c.c. tap- 

 water, 0-1 grm. (NH 4 ) 2 S04, 0-1 grm. K 2 HP0 4 and 0-2 grm. MgC0 3 

 (Winogradsky's medium), and incubating for seven days at 26° C, at the 

 end of which period the liquid showed a strong reaction for nitrate. Sub- 

 cultures were then made from this liquid into fresh nitrifying solutions, 

 and, after a further week's incubation, a second sub-culture was made, which 

 was used for testing the effect of the auximone. 



A series of eighteen flasks was then prepared, six containing normal 

 nitrifying culture solution, six the normal solution plus phosphotungstic 

 fraction from 1 grm. of bacterised peat, and six the normal solution with 

 the addition of the silver fraction. All were inoculated from the second 

 sub-culture of nitrifying organisms and incubated at 26° C. At the end 

 of 48 hours all the flasks containing auximone showed a thick scum on the 

 surface of the liquid, and when examined at the end of six days were found 

 to contain no trace of nitrate, while in those flasks without auximone, where 

 no scum had developed, nitrification had proceeded normally. Some 

 contamination of the medium was suspected, and the work was repeated, 

 great care being taken with the sterilisation of flasks and media. Again 

 a scum appeared in all the liquids containing auximone, and a third 

 experiment yielded similar results. 



