272 



DESCRIPTIVE BOTANY. 



axils of which bulblets appear. The roots are large, tuberous processes, 

 largest at the bottom, sometimes 6 feet loug, taperiug from the bottom 

 (where they are sometimes 8 inches in diameter) to the top, the crown be- 

 ing an inch in diameter, the whole tuber sometimes weighing 40 pounds; 

 edible. 



There are about 150 species known to botanists. The most important edible 

 species are the D. sativa and D. batatas, D. japonica and D. alata. 



Geography. — The yam is tropical and subtropical, though it arrives at 

 maturity in higher latitudes ; but the tubers do not reach perfection except 



under a high temperature. The geo- 

 graphical distribution of this genus is 

 a belt all around the earth, between 

 the parallels of 30° on both sides of 

 the equator. Some of the species are 

 indigenous to America, some to Africa, 

 but more to Asia. It is but recently 

 that it has been brought under cultiva- 

 tion. Its cultivation is confined prin- 

 cipally to Japan, the East India Islands, 

 and Siam. 



Etymology. — Dioscorea, the generic 

 name, was given by Linnagus in honor 

 of Dioscorides, the Greek botanist. 

 The specific name, sativa, signifies the 

 " sown," or " cultivated," plant. The 

 name batatas is supposed to signify " a 

 club," referring to the shape of the 

 tuber, which is small at the upper end 

 and large at the other. The common 

 name, yam, is supposed to be of Afri- 

 can origin, the meaning being un- 

 known. 



Use. — The yam is used for a table vegetable, and is prepared by boiling, 

 baking, frying, or roasting in hot embers. It is also beaten into a paste and 

 made into cakes ; also boiled, mashed, and made into puddings and custards. 

 It constitutes a large portion of tlie food of the savage and half -civilized tribes 

 of Africa and Malaysia. 



DiOSCOKEA SATIVA (Yam). 



Order LIX. LILIACE^. 



Flowens perfect, mostly terminal, solitary, racemose or spiked. 

 Perianth tubular, inferior ; limb 6-lobed or parted, or perianth leaves 

 distinct. Stamens 6, inserted on the receptacle or perianth-tube. 

 Ovary free, usually 3-celled ; cells few to many-seeded ; style simple 

 or 3-cleft. Fruit capsular. Leaves simple, entire, sheathing fascicled 

 at the base, and sessile on the stem, flat or channelled. Herbaceous 

 perennials, sometimes tree-like and woody. Root bulbous, tuberous, 

 or with a creeping rhizome. 



No. of genera, 187; specie>;, 2000; cosmopolitan; mostly in damp 

 places, but not in the water. 



