Agricultural Conjurers 57 



new supply be not furnished, after a while 

 the land becomes impoverished. This is 

 one reason why there are in some parts of 

 the country so many abandoned farms toe 

 little nitrogen and the atmosphere full of it. 



It has long been clear that if the farmer 

 could only directly tap the atmospheric 

 nitrogen, his fortune would be made. It 

 has been known ever since the times of the 

 old Romans that what is called " green 

 manuring," that is the ploughing under of 

 crops of leguminous plants, such as clover, 

 enriches the soil in quite a remarkable though 

 mysterious way. But the reason for this 

 common practice was left for the modern 

 bacteriologist to discover. And here enters 

 one of the most noteworthy of the bacterial 

 conjurers. 



Farmers and other students of plants for 

 a long time have been familiar with certain 

 little nodules or tubercles (Plate V.) growing 

 on the roots of leguminous plants such as 

 clover, peas, beans, etc., and had supposed 

 that they indicated some kind of disease of 

 the plant. But a few years ago it was dis- 



