398 



THE PRINCIPLES OF SOIL MANAGEMENT 



gram having been found; while in soil of ordinary 

 fertility and tilth the numbers range from 1,000,000 

 to 5,000,000 per gram. The extreme rapidity with 

 which reproduction occurs makes it possible for the 

 number to increase enormously when conditions are 

 favorable for their growth. While, therefore, very 

 few bacteria are present in soils of the northern states 

 during the winter, the number increases with great 

 rapidity in the spring. Marshall Ward has shown 

 that in the mild winters in England some soil bac- 

 teria at least continue their activity throughout the 

 winter. In the southern states of America the same 

 is doubtless true. 



The following table shows the number of bacteria 

 per gram of soil found in different parts of the United 

 States during some portion of the growing season: 



Table LXI 



