THE NITROGEN CYCLE 471 



soils than in untreated soils. There can be no doubt, 

 therefore, that, at least for some higher plants, the quan- 

 tity of available nitrogen is greater in the treated soils. 



The relation of protozoa to the ammonifying bacteria 

 is somewhat more difficult of demonstration. Methods 

 for the enumeration of protozoa in the soil are not suffi- 

 ciently well worked out to admit of an entirely satisfactory 

 study of their relation to the ammonifying bacteria. 

 However, Russell and Hutchinson do not hold that pro- 

 tozoa are necessarily the limiting factor in ammonia 

 production in normal soils, but grant that some other 

 organism of comparatively large size may be responsible 

 for this. They intimate also that not only the available 

 nitrogen, but also the quantities of other plant nutrients, 

 are limited by organisms destroyed by partial steriliza- 

 tion ; otherwise increased productiveness induced by 

 partial sterilization would be confined to soils in which 

 nitrogen is normally the limiting factor. The theory 

 docs imply, however, that plant-food is the limiting factor 

 in all soils benefited by partial sterilization under the 

 conditions of the experiment. 1 



1 Russell, E. J., and Darbishire, F. V. Oxidation in soils 

 and its relation to productiveness. Part 2. The influence 

 of partial sterilization. Jour. Agr. Sci., Vol. 2, pp. 305-326. 

 1907. 



Russell, E. J., and Hutchinson, H. B. The effect of partial 

 sterilization of soil on the production of plant food. Jour. 

 Agr. Sci., Vol. 3, pp. 111-144. 1909. 



Kussell, E. J., and Hutchinson, H. B. The effect of partial 

 sterilization of soil on the production of plant food. Part 2. 



Russell, E. J., and Hutchinson, H. B. The limitation of bac- 

 terial numbers in normal soils and its consequences. Jour. Agr. 

 Sci., Vol. r,, pp. 1.72-221. 1903. 



Buddin. W. Partial sterilization of soil by volatile and 

 non-volatile antiseptics. Jour. Agr. Sci., Vol. 6, pp. 417-451. 

 1914. 



