ABSTRACTS 555 



The Occurrence of Bacteria in Frozen Soil. E. C. Harder. (Bot. 



Gaz., 1916, 61, 507-517, two graphs.) 



Investigations were begun during the latter part of October and the 

 samples were examined every week until the latter part of February. 

 A dark, medium rich, slightly sandy garden soil was studied, obtained 

 from the University campus near the College of Agriculture at Madi- 

 son, Wisconsin. The soil was sampled to a depth of 6 inches each time. 

 The entire sample was thawed when necessary and thoroughly mixed 

 in a mortar previously washed out with 95 per cent alcohol. After 

 proper dilution, plates were poured and counted after an incubation 

 period of eight days at 28°C. Hey den Nahrstoff agar was used as a 

 culture medium. 



In order to determine whether the high bacterial content of frozen 

 soil was due to an actual increase or whether other factors brought 

 about this phenomenon, two duplicate sets of potted soils were pre- 

 pared. One set was kept at room temperature and the other set was 

 placed outside, subject to atmospheric temperatures. 



Summary of results. 1. It was found that the number of bacteria in 

 surface soil increased markedly after heavy frost, and in general main- 

 tained a high average during the winter months. The increase and 

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

 ture content. 



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

 terial count after frosts. On the contrary the enriched cultures showed 

 a distinct retardation of bacterial growth when in a frozen condition. 



3. The bacterial flora was much 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 pro- 

 portion 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 tem- 

 peratures as low as 40°C. or more below zero. The increase in num- 

 bers, however, seems to be due to mechanical transpiration of moisture 

 coming up from below during heavy frost, and where such transpira- 

 tion is not possible there is an actual retardation in growth as compared 

 with that in unfrozen soils. — J. T. E. 



Incubation Studies with Soil Fungi. S. A. Waksman. (Soil Science, 



1916, 1, 275-285.) 



Too little attention has been directed to the possible influence of 

 fungus forms as one of the important factors in soil fertility. 



The longer and more complex life cycle of the fungi no doubt makes 

 their relation to the fertihty of the soil different at successive stages 

 of growth. 



Bacteriological methods were pursued in the study of three organ- 

 isms which represent three very important groups of soil organisms: 

 Mucor plumbeus, Penicillium sp., and, Monilia sitophila. ^ 



At first the moisture relationship and incubation period were deter- 



