Effects of Auximones on Soil Organisms. 



509 



effects of this soluble humus 011 soil bacteria accordingly reproduce more 

 exactly the influence of the organic matter of soils upon the bacterial flora. 



Eecently Bottomley* has shown that a water extract of bacterised peat, 

 and certain fractions obtained therefrom, produce an increase in the growth 

 of plants which cannot be attributed to any purely nutritive effect caused by 

 the recognised manurial constituents present, and he suggested that during 

 the decomposition of the peat, certain accessory food substances are formed, 

 which fulfil a similar function to that of the vitamines known to be so 

 important in animal nutrition. His recent work on the influence of these 

 growth-promoting substances obtained from bacterised peat, which he has 

 called "auximones," has lent confirmation to this suggestion, and it was 

 with the object of investigating the effect of these auximones upon the four 

 chief groups of soil organisms concerned in the nitrogen cycle, that is, upon 

 the nitrogen-fixing, the nitrifying, the ammonifying, and the denitrifying 

 bacteria, that the present research was undertaken. 



Nitrogen Fixation. 



It was first pointed out three years ago by Bottomleyf that the addition of 

 bacterised peat to soil results in a marked increase in the rate of nitrogen 

 fixation, and this result was attributed purely to the activity of the nitrogen- 

 fixing organisms introduced into the soil with the material. HeJ has 

 since found that, apart from the organisms which the material contains, 

 the bacterised peat itself has certain inherent properties which have the 

 effect of increasing the rate of nitrogen fixation by soil organisms to a 

 marked degree, and that these properties are not possessed by either raw or 

 chemically treated peat. The experiments hitherto recorded, however, have 

 been more or less isolated, and it appeared advisable to undertake a more 

 extensive investigation of the effect of bacterised peat, and the various 

 fractions obtained from it, upon nitrogen fixation in soil and in both crude 

 and pure liquid culture. 



A preliminary experiment was carried out to determine whether 

 bacterised peat which had been sterilised at 135° C, to kill off the 

 nitrogen-fixing organisms which it contained, would stimulate nitrogen 

 fixation in soils. Six portions, each consisting of 24 oz. of a uniform 

 sample of a loamy soil, were weighed out. Two were mixed with one part 

 in ten by volume of sterilised bacterised peat, and two with a similar 



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

 t Bottomley, W. B., ' Report Brit. Assoc.,' 1913. 



% Bottomley, W. B., 'Roy. Soc. Proc.,' B, vol. 88, pp. 237-247 (1914), and vol. 89, 

 pp. 102-108 (1915). 



