﻿.016] 



HA RDER—BA CTERTA 



weather continuing to December 9, the bacterial content of the 

 soil gradually decreased to much below the original amount, the 

 lowest count of the winter, 7,459,450 bacteria per gm. of dry soil, 

 occurring during this period. At the same time the soil thawed 

 and the moisture content decreased. The count of December 15, 

 taken some days after the second frost, again showed a marked 

 increase in bacterial numbers, as well as in moisture content. 

 Following this there was a continuous cold period culminating in 

 very heavy frost from December 25 to 27. On December 29, 

 following this heavy frost, we had the highest bacterial count of 

 the winter, 38,122,523 bacteria per gm. of dry soil. The next 

 count, January 5, showed a considerable decrease with but a slight 

 decrease in moisture content. This is probably to be explained 



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by the fact that the high count of December 29 included many 

 forms that could not withstand the more severe cold to which they 

 were exposed in the upper soil layer. The low count of January 14 

 accompanied by an increase in moisture is difficult to explain. 



After this date there was no great variation in the bacterial 

 content until February 23, when there occurred a marked decrease 

 accompanying the complete thawing of the soil. During this 

 thawing, however, there was only a slight decrease in soil moisture. 

 The figure for April 13 shows the normal bacterial content of the 

 soil during the spring. 



Experiments with potted soil. — In order to determine 

 whether the high bacterial content of frozen soil was due to an 

 actual increase in growth, or whether other factors brought about 

 this phenomenon, two duplicate sets of potted soil were prepared. 



