410 MICROORGANISMS 



and to leave them in the soil in soluble compounds which are 

 available to the higher plants. 



Each of these elements has its own peculiar chemical rela- 

 tions and therefore its own peculiar relations to bacterial 

 action. Consequently, the story of the transformations of 

 each of these elements is different from every other and each 

 is quite as interesting as is the nitrogen story, but our limited 

 space will not permit us to study them. It is sufficient to say 

 that different kinds of bacteria produce in one way or another 

 many different kinds of acids. These acids attack the insoluble 

 mineral compounds of the soil and soluble compounds result. 



Foremost among these acids which result from bacterial 

 acid is CARBONIC ACID. This acid results from the chemical 

 union of carbon dioxide, liberated by the bacteria, with water. 

 Numerous other organic acids, i.e., acids which contain carbon, 

 are produced in the soil by bacteria. Not much is known of 

 the detail of the action of most of these acids on the mineral 

 compounds of the soil but there is little doubt that most of 

 them are serviceable in rendering materials available for higher 

 plants. 



Numerous other chemical reactions induced by bacteria, 

 aside from the production of acids, result in the formation of 

 available materials for the higher plants. It should be said 

 also that molds and other fungi are active in these processes in 

 the same way as bacteria are. 



467. Bacteria and Soil Leaching. It is evident that, if the 

 materials that compose the soil should remain insoluble, they 

 would, not only be unavailable to the higher plants, but they 

 would also remain where they are and would not be carried away 

 by the water as it percolates through the soil. Much of the 

 water that falls on the soil as rain, soaks in and keeps sinking 

 to deeper levels until it finally finds an outlet to some stream 

 and then makes its way to the sea. As it does this, it naturally 

 carries with it much of the soluble material that it passes. 

 In this way, the soil is constantly losing some of the very 

 elements which the higher plants need. This process by which 



