﻿BOTANICAL GAZETTE 



One-hundred gm. samples of soil thus prepared were then inoculated 

 with infusions consisting of a mixture of the fresh soils to be tested 

 and sterile water, 10 cc. of the infusion (containing in each case 

 about 5 gm. soil) being added to each 100 gm. sample. The final 

 moisture content of the soils during incubation was 20 per cent. 



Brown and Smith assert that actual multiplication in the 

 numbers of bacteria takes place in frozen soils, and that to this 

 must be ascribed the increased numbers during the winter months. 

 They present the hypothesis that, owing to the concentration of 

 various salts in the film of hygroscopic water around soil particles, 

 this film probably does not freeze under ordinary winter conditions, 

 and bacteria may live and multiply in it. 



Present investigations 



Summary of results. — During the winter of 1914-1915, the 

 writer conducted a series of experiments with field and potted 

 soils. The results obtained justify conclusions which are somewhat 

 at variance with those obtained during the recent investigations by 

 Conn at Ithaca and Geneva, New York, and by Brown and Smith 

 at Ames, Iowa; and it seems advisable, therefore, to publish them. 

 The principal results obtained 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 de- 

 creases, however, were found to bear a distinct relation to the mois- 



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

 bacterial content after frosts. On the contrary, the enriched cul- 

 tures showed a distinct retardation of bacterial growth when in a 

 frozen condition. 



3. The bacterial flora was more or less the same during the fall, 

 winter, and spring, with the exception that after heavy frosts the 

 small transparent colonies characteristic of water and of deeper 

 soils formed a larger proportion of the growth on the plates. 



From these results it seems reasonable to conclude that ordinary 

 soil bacteria undoubtedly withstand cold to a marked degree, even 

 to temperatures as low as 4 0 C. or more below zero. The increase 



