14 AGRICULTURE FOR COMMON SCHOOLS 



clover crop or a good crop of some other legume. It is the 

 bacteria which make the clover crop such a desirable one. 

 Bacteria do not live on the roots of any plants other than 

 legumes. There are other bacteria, which do not live on the 

 roots of any kind of plants and which catch nitrogen and 

 hold it for the use of plants. All bacteria which have any- 

 thing to do with gathering nitrogen are called nitrifying bac- 

 teria. They require proper conditions of temperature, moist- 

 ure, air, and food to do their work well. The farmer who 

 has ground well drained, manured, and cultivated helps the 

 bacteria to do their work. 



There are some bacteria which work well when the soil is 

 too wet to cultivate, but they are not the helpful kind. In- 

 stead of gathering nitrogen they lay hold on those substances 

 in the soil which contain nitrogen and let it loose so that it 

 escapes from the soil as a gas. Such bacteria are called deni- 

 trifying bacteria. The farmer who does not have his land 

 well drained and cultivated helps this kind of bacteria to 

 work, and they do him no good. 



