538 



General Botany 



The acacias and mimosas are largely tropical and subtropical 

 trees and shrubs, with regular flowers. The genera common to 



Fig. 342. Flowering branch of Acacia Sene- 

 gal, one of the many leguminous plants with 

 radial flowers widely distributed in the 

 tropics. In the southern United States 

 there are several common species of Acacia 

 and the closely related Mimosa. Acacia 

 Senegal is the source of gum arable. {After 

 Strashurger.) 



Fig. 



343. Peppermint {Mentha pi- 



perita). The square stems and op- 

 posite leaves are] characteristic of 

 the mint family. 



All 



temperate regions have irregular flowers like the sweet pea 

 produce the pod, opening by two sutures called a legume. 



The cactus family {Cactaceae). This group of succulent 

 desert plants seems to have originated in tropical America and 

 to have spread sparingly into the dry temperate regions both 

 north and south. There are about 25 genera and 1500 species. 

 For the most part they lack leaves and the stems are covered 



