constitute so large a proportion of the normal bacterial flora of the 

 soil. The authors then carried out various experiments, which 

 showed (l) that no stimulus could be supposed to have taken place 

 through the treatment so as to make the bacteria remaining in the 

 soil more active ; (2) that there had been no selective destruction of 

 organisms which would leave behind a population of a more active 

 type than the usual flora of the soil. By other steps which need not 

 be here set out, it became clear that the difference between the 

 treated and untreated soils was due to some factor in the latter which 

 normally limits the number of bacteria, and therefore the rate of 

 production of ammonia. Search for this unknown factor disclosed 

 the presence, in all soils so far examined, of numbers of protozoa and 

 amoeba, which live on bacteria and keep their numbers down to the 

 comparatively low limit specified. The heating or treatment with 

 antiseptics kills off all these large organisms, but leaves unhurt some 

 spores of the ammonia-producing bacteria, which afterwards can 

 develop to a much greater extent because they are freed from their 

 normal check. 



The theory as it stands then assumes that, putting aside its 

 physical characteristics, the fertility of a soil is determined by the 

 activity, or rather by the number, of its ammonia-producing bacteria, 

 and the number is kept in equilibrium by the activity of the protozoa 

 for which these bacteria serve as food. Any cause which destroys 

 or reduces the number of the protozoa enables the bacteria to extend 

 their territory, and so raises the fertility of the soil. The authors 

 have also carried out a number of collateral experiments, which show 

 that the direct additions of these large organisms will rapidly reduce 

 the activity of various fermenting media, but this and other positive 

 evidence in favour of the theory have not as yet been published. 



It is obvious that this work suggests the possibility of similarly 

 increasing the productivity of soils in the open, if the injurious 

 protozoa can be suppressed by methods that are not too costly. 

 Experiments upon these lines have been designed and will be carried 

 out during the coming season. 



"Direct assimilation of Ammonium Salts by Plants," by Drs. 

 H. B. Hutchinson and N. H. J. Miller. In this paper the authors 

 describe an investigation of the question of whether the higher plants 

 are capable of utilising ammonia directly without a previous 

 conversion into nitrates. The authors succeeded in growing peas 

 and wheat in water cultures under sterile conditions, so that neither 

 nitrification nor other bacterial changes could take place in the 

 nutrient supply. It was important to determine whether plants could 

 thus make use of ammonia without previous nitrification in view of 



