492 A TEXT-BOOK OF BOTANY. 



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 resembling rum ; various fibers, as Sisal hemp, " Hene- 

 quen " or " Sacci," etc. Other members of the Amaryllidaceae 

 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 be- 

 longing 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 {Dioscorca villosa) of the 

 United States (Fig. i8o). 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 Liliaceae, are destroyed on heating. The rhizome of 

 Tamils communis contains saponin, and Rajania subamarata con- 

 tains tannin. 



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

 ily 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. 254, 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 L^nited States. It is distinguished by its 

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

 flowers are violet-blue. The rhizome somewhat resembles that of 

 calamus, but is of a dark brown color and contains 25 per cent, of 

 acrid resins, a volatile oil, starch, and tannin. 



Iris -florentina, which yields the orris root of commerce (Fig. 

 190), is a plant cultivated in Middle and Southern Europe, and 

 closely resembles the above-mentioned species. The rhizome con- 

 tains a volatile oil resembling that found in violets, and is used 

 in perfumery. Orris root is also obtained from Iris germanica 

 and /. pallida. The violet odor is developed on keeping the rhizome 

 a vear or two. 



