200 



IMPORTANT FAMILIES OF PLANTS 



flowers mostly irregular and often showy and papilionaceous 

 (i.e., butterfly-like) ; calyx four to five cleft; corolla usually of 

 five petals which may be united (as in the case of the clover) 



or only partly united (as in 

 the pea) ; stamens unusu- 

 ally 10 with all the stamens 

 united (monadelphous) or 

 nine united, and one free, 

 but forming a tube, enclos- 

 ing the pistil; pistil one, 

 with one chamber fruit usu- 

 ally a legume or pod. 



This is one of the most 

 important families, econom- 

 ically, to be found in the 

 plant kingdom. It contains 

 nearly four hundred and 

 fifty genera and more than 

 seven thousand species, 

 many of which are impor- 

 tant agricultural crops. 

 They include cultivated 

 crops used as food for man 

 and beast; forest trees and 

 ornamentals. The growing 

 of leguminous crops is also 

 recognized as one of the best 

 methods of improving the 

 soil. 



Legumes Gather Nitrogen. The use of legumes in the 

 improvement of soils depends upon the partnership (or symbi- 

 osis) existing between these plants and certain nitrogen- 

 gathering bacteria which make their homes on the roots (Fig. 



PIG. 125. Red clover plant with nodules 

 on the roots, containing bacteria which enable 

 the plant to gather nitrogen from soil air. (Fights 

 of the Farmer.) 



