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



directly opposed to the statement by Eussell* that " a measure of the speed 

 at which nitrates are formed does not measure the rate of nitrification, but 

 the rate of ammonia production." If this statement that the oxidation of 

 ammonia to nitrates is normally proceeding as fast as ammonia is being 

 formed be true, then the possible sources of nitrifiable nitrogen must be 

 considered, for the auximones themselves introduce only a negligible 

 quantity. There is the possibility that the addition of the auximones may 

 have an effect upon ammonification in soil widely different from that in 

 liquid culture, owing to divergence of conditions ; but, apart from this 

 consideration, the fixation of nitrogen introduces an appreciable quantity of 

 this element into the soil, probably in a nitrifiable form. Thus the increase 

 in nitrate content following upon the addition of the auximone fractions to 

 the soil is probably partly accounted for by the nitrification of the element 

 introduced by the nitrogen-fixing organisms, whose activities are also shown 

 to be increased by this addition. Experiments in pure culture, however, 

 show that in the presence of sufficient quantities of nitrifiable nitrogen, the 

 activities of the nitrifying organisms are increased beyond their normal rate 

 by the addition of auximones. 



Denitrification. 



For the purpose of investigating the effect of the auximone fractions of 

 bacterised peat upon denitrification, methods of liquid culture were again 

 employed. The bacteria which are concerned in this process are responsible 

 for the loss of nitrogen which often follows upon the addition of decom- 

 posing organic manures to soil containing nitrates. Since the nitrogen is 

 liberated in the free gaseous form, an estimation of the activity of the 

 organisms can be made approximately by measuring the volume of gas to 

 which they give rise. 



For the isolation of these organisms in impure culture, G-iltay's solution is 

 most generally employed, but equally good and very uniform results have 

 been obtained during the present work with a medium consisting of calcium 

 tartrate 10 grm., potassium nitrate 10 grm., di-potassium phosphate 

 - 25 grm., and tap-water 500 c.c. This has the advantage of being simple 

 and very readily made up, so it was used throughout the following 

 experiments. 



In order to obtain a culture of the organisms, small portions of decom- 

 posing stable manure were introduced into Erlenmeyer flasks of 150 c.c. 

 capacity. The flasks were then filled to the brim with the above medium, 



* Eussell, E. J., ' Soil Conditions and Plant Growth,' 1915, p. 88. 



