CHAPTER XVII 



LEGUMES 



Lupines and vetches for forage, if cut green, and the earth plowed above 

 their roots, fertilize the lands like manure. PALLADIUS 



I. GENERAL STATEMENT 



262. The importance of legumes. The great family of plants 

 known as legumes is a necessary part of every system of agri- 

 culture. The legumes are the principal source of protein for 

 man as well as for beast. More than half the people of the 

 world eat beans, peas, and lentils instead of meat, milk, and 

 eggs. Much of the protein feed of live stock is in the form 

 of alfalfa, clover, cowpeas, and soy beans. The legumes have 

 had an important part in making our soils fertile, and they 

 have an equally important part in keeping them productive. 



263. Where legumes get their nitrogen. All the nitrogen 

 contained in corn, wheat, and other such crops comes from 

 the soil. Much of the nitrogen of the legumes comes from the 

 air. It has already been pointed out in detail how such plants 

 as the clovers and peas gather nitrogen from the air through 

 the activity of certain bacteria (Figs. 95 and 96). In the grow- 

 ing plant this nitrogen is combined with starch and mineral 

 substances, such as phosphorus, and formed into what we call 

 protein. Protein is very valuable for feeding live stock. When 

 a plant is returned to the soil as a manure, the protein it con- 

 tains is broken down ; the nitrogen is changed into the form 

 of a nitrate and is again available as plant food. 



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