280 Bacteria in Relation to Country Life 



have experimental evidence that the nitrogen-fixing 

 azotobacter are readily found only in soils well supplied 

 with lime; that most of the nitrogen-gathering, legumi- 

 nous plants prefer soils well provided with lime; that 

 decay and nitrification proceed more rapidly in lime 

 soils. In a word, then, lime is essential for the well- 

 being of the soil bacteria and its removal from the soil 

 is largely dependent on their activities. The limestone 

 strata of many countries bear witness to the far-reaching 

 results of these activities, to the important geological 

 changes caused by them and to the indirect effect on 

 the life in the sea. 



Bacterial activities and lime. — It should not be supposed, 

 however, that the activities of soil bacteria tend always 

 to decrease the amount of lime carbonate in the soil. 

 On the contrary, certain changes caused directly or 

 indirectly by bacteria tend to restore somewhat the 

 losses of lime caused by other bacterial changes. It 

 has been demonstrated that, in the decay of vegetable 

 or animal substances containing lime, the carbonate of 

 the latter may be formed. It has been found, likewise, 

 that certain compounds of lime, existing in rock frag- 

 ments and known as silicates, may be changed gradu- 

 ally to carbonate of lime under the influence of carbon 

 dioxid produced by the soil organisms. This is in accord 

 with the observations made on certain soils derived 

 from trap-rock. These soils were found to contain very 

 slight amounts of lime carbonate. Notwithstanding 

 this, the appHcation of lime seemed to do no good. It 

 is believed, therefore, that, in the gradual weathering 

 of the trap-rock with silicates of lime, sufficient amounts 



