240 BOTANY AND PHARMACOGNOSY. 



or Century plant. This is a characteristic genus of plants of the 

 hot and arid regions of North America. The best known of these 

 is the Century plant {Agave americana) which is one of the 

 most important economic plants of Mexico. The -stem axis of 

 the plant is very short and the thick fleshy leaves form a tuft at 

 the tip. The leaves are lanceolate, with spinose margins, and fur- 

 nished with stout terminal spines. The leaves as well as the 

 roots contain a large amount of mucilage which retains water and 

 thus helps to adapt the plants to these arid regions. The plants 

 grow slowly and may flower when they are ten or twelve years 

 old. 



The Agaves contain saponin and other principles of medicinal 

 value. They yield a number of other products as follows : Pulque 

 a fermented drink of the Mexicans, Mezcal a distilled drink re- 

 sembling rum ; various fibers, as Sisal hemp, " Henequen " or 

 " Sacci," etc. Other members of the Amaryllidacea? likewise find 

 use as medicines and as foods, many of them being cultivated as 

 ornamental plants, as Narcissus, Hymenocallis, Crinum and 

 Amaryllis. 



c. DIOSCOREACE^ OR YAM FAMILY.— The plants 

 belonging to this family are twining shrubs or herbs with 

 tubers either above or below ground. The general characters of 

 the plants are shown in the wild yam-root {Dioscorea villosa) of 

 the United States. Several species, notably, D. Batatas, yield the 

 YAMS or Chinese potatoes of commerce. 



Many of the species of Dioscorea, as well as other members of 

 this family contain active principles which like those of the 

 Araceae and Liliacese are destroyed on heating. The rhizome of 

 Tamils communis contains saponin and Rajania suhamarata con- 

 tains tannin. 



d. IRIDACE^ OR IRIS FAMILY.— The plants of this 

 family are perennial herbs with mostly equitant (bilateral) leaves 

 and horizontal rhizomes, or corms. The flowers are regular or 

 irregular and with a petalloid stigma (Fig. 124, B). 



Iris versicolor is a flag-like plant commonly known as the 

 LARGER blue FLAG and found abundantly in the marshes and wet 

 meadows of the Eastern United States. It is distinguished by its 

 tall stems and sword-shaped, somewhat glaucous leaves. The 



