YAM. See Dioscorea and Sweet Potato. Circular 21, 

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

 notes on the introduction of West Indian Yams (Dios- 

 coreas) to subtropical agriculture in the U. S. 



YARKOW. Consult ^c7ii7/f". 



YATE. See Eiicahjptns orriilentnlis. 



YELLOW ROOT SHRUB. Xaiilhnrrhiza. 



YELLOW-WOOD. Cladrastis tinctoria. 



YERBA BUENA. Mieromeria Douglasii. 



YEW. See Taxus. 



YOUTH-AND-OLD-AGE. Zinuia. 



its forms, and glauca are hardy in the northern states, 

 and y. Treeuleana shows considerable resistance to 

 frost. The teudi-r spccit-s art- kept in the cactus house. 

 Well-drainfd v;mi.1, I^imh -:iii ~ ihfiu l.cst, but with good 



drainage thi\ ■ ' * i lar-c t.-iti^t ..f soil and 



exposure. I'l^:' ' > .;1 -ri^, simi niitings, and 



the rhizonii'- ;.'i: ■ > i-.m,.^ i.i.i.liirr, Mlii,-h may 



be cut into si,,,tl m n^i:: - ' ■■■'■-I m >l ni. 1,,^. I.p,,,,),. 



r.'j;:r„l..n,.l I.I II- •; ■■:■ " ''I:. ■■"•.' 'M ,,!■ ns,.s. 



pectedly produce an al>undaiic-c 

 even on the smaller plants. ' 

 Y. glauca flowers in June and 

 by T. filamentosa and I', flaeri 

 T. gloriosa, which usually How 

 several years, bloom from late . 

 autumn as to be cut down by frc 



■ species, 

 followed 

 forms of 



ate in the 



■'-'■t' ,,,., 



?*/ 



1% % 



AJfe 



fc. 



L ,,»-^A\\iJ 



2761 Yucca Whipplei 



YCCCA (Indian 'naim- for the Manihot, erroneously 

 applied by Gerardi-i. I,ni,),-,.i. About a dozen species, 

 chiefly of the arid N"iih AiiMii.aii table-land and con- 

 fined to the United STaTt-s. Mcxirn and adjacent islands. 

 Evergreens with long, narrow, usually spiny-pointed 

 leaves and panicles of large white nocturnal flowers 

 frequently shaded with green or purple. 



Y, fita}ne}itosa, flaccida, baccata^ gloriosa in some of 



126 (li 



Most species may be fertilized if fresh pollen is trans- 

 ferred directly from the anther to the stigmatic cavity of 

 a newly opened flower, preferably one seated directly on 

 the main shaft, where nutrition is more certain. Y. aloi- 

 folia commonly fruits freely, but the others rarely fruit 

 spontaneously in cultivation except Y. filamentosa and 

 Y. ftaccida, which are pollinated by a small white moth 

 (Pronuba yiiccasella) that accompanies them when cul- 



