122 Practical Farming 



careless cultivation, through which it is used up, and none 

 returned to keep the work going on. This is one of the 

 most important reasons for the rotation of crops, in which 

 there shall frequently come on the soil crops like clover 

 or peas that will return organic matter to the soil, and 

 thus keep up the work of the nitrifying bacteria, which 

 can thrive only on decaying matter. 



But while all organic matter contains 

 The Agency nitrogen which the plants have gotten from 



o ac eria ^^^ ^^ji there is one class of plants which 

 Nodules on ' ^ 



Legumes '^^ their decay furnish nitrogen more plenti- 



fully, which they have gotten from the air, 

 and which, therefore, is really an addition to the nitrogen 

 of the soil. This class of plants is the one which botanists 

 call the LeguminoscB, meaning plants that make their 

 seed in legumes or pods. And here again we find the work 

 of these minute plants we call bacteria. But they are 

 bacteria that subsist on Hving and not on dead matter. 

 It has long been known to farmers that in some way the 

 growing of clover, cow peas and other legume plants, did 

 help the productiveness of the soil. It was long thought 

 that they had the power to get ammonia from the air 

 through their leaves. But carefully conducted experi- 

 ments soon proved that the leaves of the legumes had no 

 such function. It was deemed reasonable to suppose 

 that when there is ammoniacal gas in the air the leaves 

 might absorb it, but it has never been proven that they 

 do. The study of the legumes was taken up by scientific 

 men and their growth accurately observed. It was soon 

 found that when any legume did acquire more nitrogen 

 than existed in the soil in which it was grown, there were 



