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



organisms, from six series each consisting of six flasks, are typical of the 

 results with Bacillus radicicola : — 



Mgrm. 



Sucrose solution 2 - 6 



„ „ + water extract bacterised peat 7'7 



„ „ + alcoholic extract bacterised peat ... 6'5 



„ „ + phosphotungstic fraction bacterised peat ... 5*6 



„ „ + silver fraction bacterised peat 6 - 



„ „ + water extract raw peat 1'9 



The difference in the density of the cultures containing the fractions 

 from bacterised peat, and those containing only sucrose, or sucrose with raw 

 peat, was very marked throughout the experiments, and afforded a very sure 

 indication of the greater activity of the organisms in those cultures containing 

 the auximone fractions. 



Both from these experiments and from those with Azotobacter, it is 

 evident that certain organic substances, the nature of which has not yet 

 been investigated, can be separated from the prepared peat, and that these 

 substances have an appreciable effect upon the rate of nitrogen fixation by 

 these organisms. 



Nitrification. 



Experiments on the second group of bacteria concerned in the nitrogen 

 cycle, that is, the nitrifying organisms, were also carried out in soil and in 

 liquid culture. Ever since the isolation, in purely inorganic media, by 

 Winogradsky,* of the particular organisms concerned, the effect of organic 

 matter upon the rate of nitrification has provoked a considerable amount of 

 discussion. Winogradsky* himself stated that the presence of nitrogenous 

 organic matter is inhibitory to the organisms, but further investigation by 

 Miintz and Lain^f revealed the fact that humus in soil has no deleterious 

 effect upon the process. Very soon Coleman^ showed that organic matter is 

 injurious only in culture solutions, and subsequent research by Stevens 

 and Withers§ fully confirmed this statement, and proved that in soils 

 the presence of organic matter may even help the process. Karpinski and 

 Niklewski|| have further stated that the presence of small amounts of some 



* Winogradsky, 'Ann. de l'lnst. Pasteur,' vol. 4, 1. Mem., pp. 213-231 ; 2. Mem., 

 pp. 257-275 ; 3. Mem., pp. 760-771 (1890). 



t Miintz and LainS, ' Compt. Bend.,' vol. 142, pp. 430-435 (1906). 



X Coleman, « Centr. Bakt. Par.,' Abt. II, vol. 20, pp. 401-420 (1908). 



§ Stevens and Withers, 4 Centr. Bakt. Par.,' Abt. II, vol. 27, pp. 169-186 (1910). 



|| Karpinski and Niklewski, ' Bull. Acad. Sci. Cracovie,' 1907, pp. 596-615. 



