710 



TEXTBOOK OF BOTANY 



fertilizers, glue, stock feed, water paints; candles, disinfectants, glycerin, 

 enamels, soaps, rubber substitutes from soybean oil; human foods in- 

 clude breakfast foods, flour, vegetable milk, butter substitutes, ice cream 

 cones, coffee substitutes, candies, chocolate, soy sauce, and seasoning 

 powders. 



The cactus family (Cactaceae). The cactus family comprises about 

 100 genera and 1500 species. The plants appear to have originated in 

 Mexico and Central America and to have migrated both north and south 

 into dry subtropical and temperate regions. Only one genus of cactus 



Fig. 347. A cactus (Opimtia) in bloom. 



(Rhipsalis) is native to Asia and Africa; it is a tropical epiphyte. Most 

 cacti are succulents and are to be found in semi-arid areas. They include 

 such familiar plants as the prickly pear (Fig. 347), night-blooming 

 cereus, sahuaro, cholla, barrel cactus, and organ-pipe cactus. 



The stems are thick and succulent, reaching a maximum height of 

 some 40 or 50 feet in the sahauro; thev are invariably spiny, and often 

 leafless. The roots are generally shallow, but widely extended in the 

 upper few inches of soil. The stems are green and contain large water- 

 storage tissues. The amount of water that accumulates in a large-sized 

 cactus may be as much as 30 tons, and the water is frequently 70 to 



