796 XV. DIOSCOEE^E. 



FLOWERS -dioecious. PERIANTH superior, 6-merous, 2-seriaie. STAMENS 6. OVARY 

 inferior, with three 2-\-ovuled cells ; OVULES pendulous, superimposed, anatropous. 

 CAPSULE or BERET. SEEDS compressed, winged, or globose, albuminous. Twining or 

 sarmentose HERBS, with tuberous rhizome. LEAVES reticulate-veined. 



Perennial HERBS, or UNDERSHRUBS, twining from right to left ; rhizome subter- 

 ranean, tuberous, fleshy, or eptgeal, and covered with a thick and regularly cleft 

 suberose bark (Testudinaria), giving off annual branches at the top. LEAVES alter- 

 nate or sub- opposite, petioled, simple, palminerved, nerves reticulate, entire or 

 palmisect; petioles often biglandnlar at the base, and often producing bulbils or 

 large tubers at their axils. FLOWERS dioecious by arrest, small, inconspicuous, 

 regular, in axillary racemes or spikes. PERIANTH herbaceous or sub-petaloid, 

 superior in the ? flowers; limb with 6 segments, 2-seriate, equal, persistent. 

 STAMENS G, inserted at the base of the perianth- segments ; in the ? 0, or rudimen- 

 tary; fdaments short, free; anthers introrse, 2-celled, shortly ovoid or globose, dorsi- 

 fixed, dehiscence longitudinal. OVARY inferior, 3-celled ; styles 3, short, often co- 

 herent at the base ; stigmas obtuse, or rarely emarginate-bilobed ; ovules solitary 

 or geminate, pendulous, superimposed at the central angle, anatropous. FRUIT 

 sometimes membranous, capsular, 3-gonous, 3-celled, opening at the projecting 

 angles loculicidally (Dioscorea) ; sometimes 1-celled by the arrest of 2 cells, the third 

 fertile, winged (Rajania) ; sometimes an indehiscent berry, 3-celled, or 1-celled by 

 obliteration of the septa (Tamus). SEEDS compressed, and often winged in the 

 capsular fruits, globose in the berried ; albumen fleshy and dense, or cartilaginous. 

 EMBRYO small, included, near the hilum, thinner and auricled at the upper end 

 (Dioscorea, Rajania), or oblong-cylindric (Tamus)', radicle near the hilum. 



PRINCIPAL GENERA. 

 * Pioscorea. Rajania. Tamus. * Testudinaria. 



Dioscorea nre very near Smilax in the nervation of the leaves, the perianth, androecium, fleshy fruit, 

 &c., but are distinguished by the inferior ovary. They differ from Taccaccte (see p. 782) in habit, 3- 

 celled 1-2-ovuled ovnry, and the internal structure of the seed; like Taccacete, they have some points of 

 resemblance with Aristolochica;. 



Dioscorea inhabit especially southern tropical and extra-tropical regions ; they are much rarer in 

 northern temperate latitudes. Rajania is peculiar to tropical America. Tamus inhabits woods in tempe- 

 rate Europe and Asia. Dioxcorea is met with in the tropics, and in temperate Australia; one small species 

 has recently been discovered in the Pyrenees (D. pyrenaicd). Testudinaiia is peculiar to South Africa. 



The root-tuber of Dioscoreee, often called Ubi, Ufi, or Papa (names given by the Americans to the 

 Potato), is filled with an abundant starch, mixed with an acrid and bitter principle. I), sntica, alata, penta- 

 phylla, bulbifera, Batatas, &c. are cultivated throughout the tropics, and contribute largely to the sus- 

 tenance of the Malays and Chinese, and the natives of Oceania and West Africa. The leaves of some 

 species are used in intermittent fevers. The tuber of Tamus communis was formerly used as a purgative 

 and diuretic ; resolvent qualities were also attributed to it, and it was rasped, and applied as a plaster on 

 arthritic strumous tumours, and on bruises whence its name of Beaten Woman's Herb. The shoots, 

 deprived of their acridity by boiling, are eaten like Asparagus. 



