BACTERIA OF THE SOIL 



283 



her of bacteria in various soils, both in a vegetative and spore 

 condition, are shown in the following table : 



BACTERIA IN SURFACE LAYERS OF SOIL 



There is a marked vertical distribution of the bacteria in 

 the soil. The greatest number are in the first six inches and 

 after a depth of one foot the number falls off very rapidly. 

 Comparatively few bacteria, either in the vegetative or spore 

 state, are found at depths over five or six feet. 



The Species of Bacteria. The bacteria of the soil are 

 mainly saprophytic in nature and are associated with the 

 processes of putrefaction and decay. A great many are also 

 merely saprophilic ; that is, they require dead organic matter, 

 but are not largely concerned in its decomposition. There 

 are a few pathogenic or disease-producing bacteria which 



