﻿BOTANICAL GAZETTE 



Conn's experiments dealt mainly with the number of bacteria 

 in frozen soils, which he compared with the number in the same soils 

 when in an unfrozen condition. He worked both with field and 

 with potted soils and reached the following conclusions: (i) "the 

 increase in number of bacteria after freezing is not due to the in- 

 crease in soil moisture which usually occurs in winter"; (2) "the 

 same increase 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"; and (3) this 

 phenomenon is probably "due to an actual growth of bacteria after 

 the soil is frozen." 



The experiments were performed with the samples of field 

 soil taken from plates prepared for the purpose, both aerated and 

 unaerated soils being examined. Each type of soil, therefore, 

 probably had a nearly uniform bacterial content originally through- 

 out its mass, and the changes that occurred in it from time to time 

 must be ascribed to the effect upon it of changes in the atmosphere. 

 Unfortunately, samples were taken only at irregular intervals, so 

 that, while the results show a general higher content of bacteria 

 in frozen soils during the winter, they are not sufficiently detailed 

 to show definitely when such increases occurred and to what they 



It is suggested that possibly freezing may have the effect of 

 breaking up compact colonies which under ordinary conditions 

 would not separate into individuals, thus making the increase only 

 an apparent one, owing to more individuals producing separate 

 colonies on the plates. This view is discarded, however, be- 

 cause upon the thawing of the soil the number of bacteria again 

 decreases to practically what it was before freezing. It is claimed 

 also that the maximum number is reached several weeks after a 

 frost. 



Conn concluded, therefore, that the increase is due to actual 

 multiplication, and the supposition is that such multiplication 

 takes place in certain denser portions of the soil solution, which, as 

 suggested by Brown and Smith (loc. cit.), probably do not freeze. 

 It is suggested that conditions in these unfrozen portions may 

 favor the growth of certain proline kinds of bacteria and suppress 



