176 



THE PULSE FAMILY LEGUMINOSAE. 



This is a very large family and contains many well-known trees, 

 shrubs, and herbaceous plants. It comprises about 460 genera with 

 7,350 species of which number more than 100 genera with about 1,400 

 species are native to North America. The flora of Pennsylvania com- 

 prises about 32 genera with approximately 90 species but only 4 spe- 

 cies belonging to 4 different genera can be classified as trees. Some 

 authors separate the members of this family into 3 distinct families 

 known as: (1) The Mimosa family, Mimosaceae, (2) The Senna fam- 

 ily, Caesalpiniaceae, and (3) The Pea family, Fabaceae. 



Many domestic and foreign plants which belong to this family are 

 of considerable economic importance. Some of our native trees pro- 

 duce very heavy, hard, and strong wood. They possess additional 

 merits in that they grow rapidly and are well adapted to artificial 

 propagation. Some of them, in particular the Common Locust, are 

 subject to the attack of destructive insects and fungi. Some of the 

 shrub members of this family are among the most attractive that one 

 can find for ornamental planting. The herbaceous members com- 

 prise some of the commonest and most valuable food and forage 

 plants of the world, such as the peas, beans, clover, and the common 

 peanut. Among the valuable products which some of the foreign 

 members of this family produce one can mention Senna and Log- 

 wood. Senna is prized on account of its laxative properties and is 

 derived from the leaves of a few African species of Cassia. Log- 

 wood, the most important of vegetable dyes, is derived from the 

 heartwood of the trunk and roots of a tree growing in the West Indies 

 and Central America. Indigo, one of our important and widely used 

 dyes, is also obtained from a member of this family. The well-known 

 Sensitive Plant (Mimosa pudica L.) so common in our greenhouses 

 and a mere weed in the tropics is one of the most widely known and 

 interesting representatives of this family. In addition they comprise 

 a great number of plants which are important on account of the medi- 

 cinal properties derived from them. Probably one of the greatest 

 values which we can attach to some of the members of this family 

 is the means which they have at their command for restoring nitrogen 

 to barren land. If one examines the roots of clover, alfalfa, soy 

 bean, or the Common Locust he may find little swellings or enlarge- 

 ments upon them known as root tubercles. These swellings are 

 caused by bacteria which possess the power of taking free nitrogen 

 from the air and by means of complicated chemical changes passing 

 it to members of this family. As a result these plants can be grown 

 upon soils very deficient in nitrates. In addition they will return 

 sufficient nitrogen to the soil so that companion or subsequent crops 

 will thrive which would have barely existed without the nitrogen. 

 The Common Locust often thrives on old abandoned mud-dams found 



