204 



BOTANY. 



112, A) are often very showy, so that many species are culti- 

 vated for ornament and are familiar to every one. The beau- 

 tiful night-blooming cereus, of which there are several species, 

 is one of these. A few species of prickly-pear (Opuntia) occur 

 as far north as New York, but most are confined to the hot, 

 dry plains of the south and southwest. 



FIG. 112. Calyciflorse, Opuntiese (Passiflorinss') . A, flower of a cactus, 

 Mamillaria (Cactacese) (from "Gray's Structural Botany"). B, leaf and 

 flower of a passion-flower, Passiflora (Passifloracese) , x %, t, a tendril. C, 

 cross-section of the ovary, x 2. D, diagram of the flower. 



The fourth order (Passiflorince) are almost without excep- 

 tion tropical plants, only a very few extending into the 

 southern United States. The type of the order is the passion- 

 flower (Passiflora) (Fig. 112, B), whose numerous species are 

 mostly inhabitants of tropical America, but a few reach into 

 the United States. The only other members of the order 

 likely to be met with by the student are the begonias, of 

 which a great many are commonly cultivated as house plants 



