Ivanderleck] bacteria OF FROZEN SOILS 31 



moisture during April. As this field was not frozen for any length 

 of time the importance of this early winter increase of bacteria is 

 evident. 



Experiment III (3). Cnltivated Soil kept Fallow for Two Seasons. 



This field was not more affected by frost than the black muck 

 field mentioned above. Low bacterial counts were recorded through- 

 out the experiment, although at times the moisture percentage passed 

 40%-. The only difference between this field and the black muck 

 field is the absence of raw material in the former. If the theory is 

 correct that the January increase in bacteria is due to the decom- 

 position of raw material, the absence of such material must exclude 

 this bacterial activity and increase. 



Experiment III (4). 



The plot was selected in a field planted to timothy for the second 

 year. The highest numbers of bacteria were counted in January. 

 At the end of March the frost line had descended to 20 inches, but 

 the numbers of bacteria had decreased. The observations were not 

 numerous enough to give an exact idea of the increases and decreases 

 in the number of bacteria present throughout the winter months. 

 Judging by experiment I and others, the January increase was due 

 to the decomposition of raw material (plant roots, etc.). The bac- 

 terial counts for the frozen soil at the end of March are decidedly 

 higher than the same counts for the unfrozen soil just mentioned 

 above (Experiment III, 3), so that there is a possibility that bacteria 

 multiplied in the frozen soil. 



Some of the diagrams of Plate III are drawn on a large scale as 

 the changes in bacterial numbers were slight. 



Conclusions. 



1. In soil containing raw material available for decomposition 

 large numbers of bacteria were counted during January. 



2. In soil devoid of raw material (soil kept fallow) no such bac- 

 terial increase was observed. 



3. Some high bacterial counts were accompanied by a high mois- 

 ture percentage of the soil. 



4. As soon as frozen soil thawed the bacteria decreased in 

 numbers. 



