Masterpieces of Science 



within twenty years as one of her least suspected 

 marvels. It is no other than that certain para- 

 sites of field and meadow so far from being hurt- 

 ful, are well worth cultivating for the good they, 

 do. For a long time the men who devoted them- 

 selves to the study of peas, beans, clovers, and 

 other plants of the pulse family, were confronted 

 with a riddle they could not solve. These plants 

 all manage to enrich themselves with compounds 

 of nitrogen, which make them particularly val- 

 uable as food, and these compounds often exist in 

 a degree far exceeding the rate at which their 

 nitrogen comes out of the soil. And this while 

 they have no direct means of seizing upon the 

 nitrogen contained in its great reservoir — the 

 atmosphere. Upon certain roots of beans and 

 peas it was noted that there were little round 

 excrescences about the size of a small pin's head. 

 These excrescences on examination with a micro- 

 scope proved to be swarming with bacteria of 

 minute dimensions. Further investigation abund- 

 antly showed that these little guests paid a hand- 

 some price for their board and lodging — while 

 they subsisted in part on the juices of their host 

 they passed into the bean or pea certain valuable 

 compounds of nitrogen which they built from 

 common air. At the Columbian Exposition, of 

 1893, one of the striking exhibits in the Agri- 

 cultural Building set this forth in detail. Vials 

 were shown containing these tiny subterranean 

 aids to the farmer, and large photographs showed 

 in natural size the vast increase of crop due to 

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