440 GENERAL MORPHOLOGY OF PLANTS 



ment, as the wistaria, sweet pea, etc. The sensitive plants 

 (Mimosa) also belong here. Peas and beans are important 

 garden and field crops, there being many varieties. The peas 

 originated from southern Europe and Asia. The lima bean was 

 originally a native of South America, as well as the kidney bean, 

 from which the common bean originated. The peanut (also 

 called " ground nut " and " goober ") is also a native of South 

 America, probably Brazil. It is extensively cultivated in the 

 Carolinas, Georgia and Tennessee. After the flowers fall the 

 pod turns downward and pushes into the loose soil where the 

 peanut matures. The clovers (Trifolium) are important forage 

 plants, the red clover being the most important. The clovers, 

 especially the white clover, are visited by bees for honey, and 

 white clover honey is one of the most prized kinds. Alfalfa is 

 related to the clovers and is also an important forage crop, espe- 

 cially in arid regions where the land is irrigated. The clover and 

 alfalfa, as well as peas, are often used for " green soiling," and all 

 of the leguminous plants are valuable for enriching the soil in 

 nitrogen because of the presence of the nitrogen fixing organisms 

 which cause the tubercles or knots on the roots (paragraph 203). 

 There are some valuable trees in the order, especially the common 

 locust (Robinia) valuable for timber because of its great dura- 

 bility. The honey locust (Gleditsia) is noted for its thorns and 

 is cultivated for ornament. The red bud (Cercis) is grown for 

 ornament, and is remarkable for the numerous dark red flower 

 buds which open before the leaves appear. 



593. Flax. The flax (Linum usitatissimum) is a member of 

 the flax family (Linaceae) and is an important fiber plant. The 

 fiber is separated from the stem and is used to make linen thread 

 and cloth, while linseed oil is obtained by pressure from the seed. 

 This flax is native in the Mediterranean region and has been 

 cultivated from very early times. It has been long cultivated in 

 the United States for oil, and recently for fiber in a number of 

 the northwestern states. Russia leads the world in the amount 

 of flax grown, while Belgium produces the finest fiber. Several 

 species of -wild flax are native to the United States. 



