YAM. See Dioscorea and Sweet Potato. Circular ">i 

 Div. of Hot., U. S. Dept. Agric., has valuable cultural 

 notes on the introduction of West Indian Yams (Dios 

 coreas) to subtropical agriculture in the U. S. 



YAKKOW. Consult Achillea. 

 YATE. See Eucalyptus occidentalis. 

 YELLOW BOOT SHRUB. Xanfhorrhiza. 

 YELLOW-WOOD. Cladrastis tinctoria. 

 YEBBA BUENA. Micromeria Douglasii. 

 YEW. See Taxus. 

 YOUTH-AND-OLD-AGE. Zinnia, 



Us forms and glauca are hardy In the northern states, 

 frot Th Tr ' cu l eana show considerable resistance to 



WP] ',.r e i end ^ S ? ecie " are ke P t in the cact " housed 

 Well-drained sandy loam suits them best. l,,,t with good 

 drainage they are tolerant of a large range of soil 

 exposure. Prop, by seeds, offsets, stem -cutting, wd 

 the rhizomes that several species produce, which may 

 be cut into short lengths and rooted in the cutting bech 



, wS CM ? n b '9 ms xi lsually in March in plant houses, 

 as when wild, and the Mexican species when brought to 

 flower are usually S pringbloo,n,rs, !,m , H .v iSmSSul 

 Lf T, Cr r ng P eriod and then suddenly and unex- 

 pectedly produce an abundance of simultaneous bloom, 

 even on the smaller plants. Of the hardy specie 

 Y. glanea flowers in June and it is quickly followed 

 by Y hlamentosa and F. flaccida, while the forms of 

 1-. 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. 



.'/:*;. > 



J761. Yucca Whipplei. 



YtJCCA (Indian 'name for the Manihot, erroneously 

 pplied by Gerarde). Lili&cece. About a dozen species, 

 hiefly of the arid North American table-land and con- 

 ned to the United States, Mexico and adjacent islands, 

 ivergreens with long, narrow, usually spiny-pointed 

 taves and panicles of large white nocturnal flowers 

 requently shaded with green or purple. 



Y, filamentosa, flaccida, baccata, gloriosa in some of 



Most species may be fertilized if fresh pollen is trans- 

 ferred directly from the anther to the stigmatic cavity of 

 anewly opened flower, preferably one st-attil dir.-<-tly on 

 the mnin shaft, where nutrition ismorecfrriiin. }'.nloi- 

 folia commonly fruits fn-Hy, but the others rarely fruit 

 spontaneously in cultivation except 1". filamentota and 

 }'. f/nrcida, which are pollinated by a small white tnth 

 (Protwba yuccastlta) that accompanies them when cul- 



126 



(1999) 



