212 EVOLUTION OF PLANTS 



eral native species of Aralia, including the ginseng, may 

 be mentioned. The Umbelliferse are mainly inhabitants 

 of the northern hemisphere and are all closely related. 

 Both of these families are distinguished by the arrange- 

 ment of their usually inconspicuous flowers in umbels 

 hence they are united with the allied family Corna- 

 ceae (dogwoods) into a common order Umbelliflorse. 



Two of the most specialized orders are the Passi- 

 florinae (passion-flowers and their allies) and the Cac- 

 taceae. The latter is a very peculiar group of American 

 desert plants ; the former are also largely American, 

 but belong principally to the moist tropical regions. 



The last order of the Calycifloree is a very important 

 one, the Leguminosae, including the beans, peas (Fig. 

 51, F, G), and other leguminous plants. Of the three 

 families, two, the Mimoseae, of which various species of 

 Acacia and Mimosa are cultivated, and the Caesalpineae, 

 of which the honey-locust (Gleditschia) and the red-bud 

 (Cercis) may be mentioned as native, are mainly tropi- 

 cal, while the other and much larger family, Papiliona- 

 ceae, includes most of the numerous Leguminosae of 

 temperate regions. The characteristic butterfly-shaped 

 flowers of these plants, and their pod-shaped fruits, are 

 too familiar to need further description. 



THE SYMPETAL^E 



The Dicotyledons which have just been considered 

 either have the petals entirely separate or quite absent. 

 There is a second division, including the most specialized 

 as well as the larger number of the Dicotyledons, in 

 which with very few exceptions the petals are more or 



