YAM, a term usually applied to the tubers of various species of Dioscorea. These are plants with thick tubers (generally a development of the base of the stem), from which protrude long, slender, annual climbing stems, bearing alternate or opposite, entire or lobed leaves and unisexual flowers in long clusters. The flowers are generally small and individually inconspicuous, though collectively showy. Each consists of a greenish bell-shaped or flat perianth of six pieces, enclosing six or fewer stamens in the male flowers, and surmounting a three-celled, threewinged ovary in the female flowers. The ovary ripens into a membranous capsule, bursting by three valves to liberate numerous flattish or globose seeds. The species are natives of the warmer regions of x>th hemispheres. According to Professor Church's analysis of the Chinese yam, it contains more nitrogenous matter, but less starch, than sotatoes: in 100 parts there are of water 82-6, starch 13-1, albumen 2-4, fat 0-2, woody fibre 0-4 and mineral matter 1-3 parts.
D. saliva and D. alata are the species most widely diffused in Topical and subtropical countries. D. aculeata, grown in India, Cochin China and the South Sea Islands, is one of the best varieties. 0. Batatas, the Chinese yam, is hardy in Great Britain, but the great depth to which its enormous tubers descend renders its cultivation unprofitable. It has deeply penetrating, thick, club-shaped, fleshy roots, full of starch, which when cooked acquire a mild taste like that of a potato ; they grow 3 ft. or upwards in length, and sometimes Yam (Dioscorea Batatas). Branch about J nat. size. Root much reduced.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)