YAM. The name yam properly belongs to the mem- 

 bers of the genus Dioscorea, although unfortunately 

 it has been applied for many years in the United States 

 to the large varieties of the sweet potato, Ipomaea 

 Batatas. The name as applied to the sweet potato is 

 thought by some to be a corruption of an African word 

 pronounced "nyam," brought by the negroes who were 

 transported to America in the early days. This word 

 was used for the true yam or other large roots or 

 tubers used for food in Africa and was bestowed by the 

 negroes on the large sweet potatoes in America. 



The botany of the cultivated yams has not been 

 cleared up. Many varieties are of mediocre qualitv, 

 while some are excellent, 

 being superior in flavor and 

 mealiness to almost any 

 other starchy vegetable. 

 Single roots or t ubers of some 

 varieties, particularly of D. 

 (data, attain great size, oc- 

 casionally even reaching 100 

 pounds or more in weight, 

 and several feet in length. 

 The best varieties, however, 

 are of small size, often less 

 than a pound in weight. 

 Among the best known of 

 these are the yampis of 

 Jamaica and the Isthmus of 

 Panama, and other varieties 

 of similar quality, such as 

 the cush-cush of the Island 

 of Trinidad. The Chinese 

 vam or cinnamon vine, D. 

 Batatas, is of excellent flavor, 

 but on account of its deep- 

 growing habit is very diffi- 

 cult to dig. Several kinds 

 of yam are grown scatter- 

 ingly in Florida. For further 

 discussion, see Dioscorea. 

 ROBERT A. YOUNG. 



YARROW: AchiBea. 

 YELLOW-WOOD: Cladnsti*. 

 YEW: Taxvs. 



YUCCA (Yuca, native name for the manihot or cas- 

 sava, erroneously applied to the present plants by 

 Gerarde). Ltiiacex, tribe Yucceae. Bold stiff-leaved 

 plants suitable for lawn planting, subtropical massing, 

 and a few of them for flower-garden use. 



Acaulescent to arboreous endogens with fibrous 

 evergreen sword-shaped Ivs. usually pungent and often 

 denticulate or fibrous on the margin: fls. white or 

 shaded with cream or violet, cup- or saucer-shaped, 

 usually pendent in large usually erect panicles, opening 

 at night and then somewhat sickishly fragrant; pol- 

 lination rarely occurs except through the aid of a 

 small white moth, Pronuba yuccasetta, found wherever 

 yuccas occur wild on the continent, which deliberately 

 gathers the pollen and thrusts it into the stigmatic 

 chamber, its larva? feeding exclusively on the maturing 

 seeds of these plants: fr. either capsular and erect or 

 fleshy and hanging in the principal groups or sub- 



genera. About 30 species, confined to N. Amer. and 

 the W. Indies, most of them native to the arid S. W. 

 TJ. S. and the Mexican tableland. A few species have 

 been cult, for centuries, and within the last decade a 

 large number of artificial hybrids have been produced 

 and intro. into cult., especially along the Medit. There 

 are recent monographs by the writer in Rep. Mo. Bot. 

 Card., VoL 13, pp. 42-116, with illustrations, and by 

 Molon in a small manual "le Yucche," Milano, 1914, 

 in which many of the Sprenger hybrids are also figured. 

 See Hesperoyucea, Samuela. 



Propagation is by seeds, offsets, stem-cuttings or 

 rhizome-cuttings. These should be planted in well- 



4019. Yucca glauca in Colorado. 



drained sandy loam, usually in the succulent house. 

 The only species hardy where frost is severe are Y. 

 glauca, Y. jilamentosa, Y. flaccida, Y. baccata, Y. 

 recwrvifolia, and Y. glonosa, which flower in the sequence 

 given, the last-named often blossoming late in autumn. 

 Y. Treculeana shows considerable resistance to frost. 

 The tender species are kept in the cactus house. Well- 

 drained sandy loam suits yuccas best, but with good 

 drainage they are tolerant of a large range of soil and 

 exposure. Y. Treculeana blooms usually in March in 

 plant-houses, as when wild, and the Mexican species 

 when brought to flower are usually spring bloomers, 

 but they often refuse to flower for long periods and 

 then suddenly and unexpectedly produce an abundance 

 of simultaneous bloom, even on the smaller plants. 

 Of the hardy species, Y. glauca flowers in June and it is 

 quickly followed by Y. filamentosa and Y. flaccida, 

 while the forms of Y. gloriosa, which usually flower 

 only at intervals of several years, bloom from late 

 August to so late in the autumn as to be cut down by 

 frost. The only well-known yucca in northern gardens 



(3529) 



