﻿5i6 



BOTANICAL GAZETTE 



kept outside, so that while the original moisture content was the 

 same, when the counts were made the amount of moisture present 

 in the jars kept outside was nearly double that in the jars kept in 

 the room. 



The results recorded in table II show clearly the retardation in 

 growth which was caused by cold and frost. In the case of jars 

 nos. i and 2, the number of bacteria per gm. of soil is almost the same 

 in the two samples, yet sample no. 2 has only slightly less than twice 

 as much moisture as sample no. 1. Jars nos. 3 and 4 show the 

 retardation even better. Here 1 per cent of dextrose was added 

 so as to produce a rapid growth. No. 3 with a much lower moisture 

 content than no. 4 shows a much greater increase in growth. This 

 is the reverse of what might be expected to happen under ordinary 

 conditions, and must be ascribed to the action of frost, since 

 normally the bacterial content should rise with an increase in 

 moisture. Jars nos. 5 and 6 gave results similar to jars nos. 1 and 

 2, the number of bacteria being slightly higher because of the higher 



In general these figures show that even a much higher moisture 

 content was not sufficient to counteract the retarding in growth 

 due to cold. 



Types of bacteria in frozen soil 



No detailed study of the varieties of bacteria in the soil was 

 made, since this would have required much more time than was at 

 the writer's disposal. Nevertheless, general differences in the kinds 

 of colonies present in successive counts were noticed. 



Usually the plates contained a varying number of raised colonies 

 of yellow, red, and fluffy white actinomycetes, a few spreaders 

 of the B. mycoides type, some red or yellow chromogens, numerous 

 small, slow-growing, transparent colonies, and many white or 

 cream colored colonies without distinctive marks, some of them 

 raised and others flat. Occasionally the plates showed a few 

 opalescent colonies. 



So far as could be noticed from the examination of colony 

 growths, there was no distinct difference between the fall, winter, 

 and spring floras. It was noticeable, however, that the relative 



