CHAPTER XIX 



HOW THE LEGUMES AID US 



THE great family of plants known to botanists 

 under the name of Leguminosce comprises 

 herbs, shrubs and large trees, and it has long 

 been known that these plants do in some way help the 

 fertility of the soil. 



For years it was contended that the herbaceous legumes 

 like clover and cow peas absorbed ammoniacal gases from 

 the air and in this way added nitrogen to the soil. But 

 long conducted experiments tended to show that there is 

 no such absorption of ammonia from the air, though the 

 late Doctor Gray once said that he could not see why 

 plants should not absorb gaseous ammonia in the air, 

 but that there was no proof that they did so. 



But the studies of biologists finally demonstrated that 

 the acquisition of combined nitrogen in the plants of this 

 family was the result of the growth on their roots of certain 

 microscopic plants known as bacteria. These bacteria 

 are truly parasitic on the roots and by their presence cause 

 an abnormal swelling on the roots forming small knots or 

 nodules in which the bacteria live. 



It has never been proven that there are distinct species 

 of these bacteria on the roots of different legumes, but by 

 long association with certain species of legumes many of 



268 



