PART VII. DISTRIBUTION OF 

 BACTERIA 



CHAPTER XXV 

 BACTERIA or THE SOIL 



Distribution according to Habitat. Some plants are 

 localized and appear only under certain conditions, while 

 others are more cosmopolitan, and what is true of plants and 

 animals is true also of bacteria. It is a matter of some con- 

 siderable importance to know the relation of bacteria to cer- 

 tain locations. At first thought it might be supposed that 

 bacteria were evenly distributed in nature, but this, as has 

 been said, is not true. 



Bacteria of the Soil. The bacteria find conditions favor- 

 able for growth in the soil, and the upper layers of the surface 

 of the earth teem with them. The greasy feel which the earth 

 has and with which everyone is familiar is due, in large 

 measure, to the bacteria which it contains. Of course, certain 

 parts of the surface soil are much more abundantly supplied 

 with bacteria than other parts ; the laws governing this will 

 be discussed as we proceed, but in a general way the number 

 of organisms in any particular soil depends upon the amount 

 of food substance, or humus, which is present. A great many 



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