16 THE ROYAL SOCIETY OF CANADA 



of bacteria is in the ascendancy in winter from that which is 

 benefited by the warm weather of summer; and it may be the 

 hostile effect of the summer organisms which prevents the other 

 types from multiplying rapidly in warm weather. In that case 

 the increase in frozen soil is not due directly to the low temper- 

 atures but to the depressing effect of the cold upon that group 

 of bacteria which is able in summer to keep the winter bacteria 

 in check." 



After his experiments in 1913 which were a continuation and an 

 elaboration of the ones mentioned abo\-e, Conn expresses the following 

 opinion: — 



1. "The number of bacteria in frozen soil is generally larger than in 



unfrozen soil. This fact was first noticed by the writer in 1910-1 1 

 when connected with the Cornell University Agricultural Exper- 

 iment Station. Recently it has been observed at a different 

 locality and in two other soils, one very different from the first. 

 It is true not only of cropped soil, as shown in the previous 

 work, but also of sod and fallow soil. 



2. The increase in number of bacteria after freexing is not due to the 



increase in soil moisture which usually occurs in winter. 



3. The same increases in germ content may take place in potted soil, 



where there is no possibility that the bacteria are carried up 

 mechanically from lower depths during the process of freezing. 



4. The facts noted under the headings 2 and 3 make it very probable 



that the phenonenon is due to an actual growth of bacteria 

 after the soil is frozen. Its influence on fertility is still an un- 

 known factor. 



5. The results given in this bulletin were obtained in a different 



laboratory and under quite different conditions from those prev- 

 iously reported, thus partly eliminating errors which might have 

 crept in because of peculiarities of technique. 



Esten, Brown and Smith agree with Conn's observations, but 

 Harden cannot endorse Conn's conclusions. His principal observa- 

 tions were as follows: — 



1. "It was found that the number of bacteria in surface soil increased 



markedly after heavy frosts and in general maintained a high 

 average during the winter months. The increases and decreases, 

 however, were found to bear a distinct relation to the moisture 

 content. 



2. The potted soils failed to show such marked increase in bacterial 



content after frosts. On the contrary, the enriched cultures 



