359 



of this 1100(1. Soiiio of the more iiitorostiui; facts are particularly well 

 oxeiiii»lifio(l ill our orcbids, to the j)hilosopliic study of Avhich Darwin's 

 iiiiportant work "On the Fertilization of Orchids" gave a distin(;t 

 impulse. But here we have adaptation of tlie plant only, and with 

 scarcely an exception most flowers, including those of our orchids, may 

 1)0 fertilized by diiferent insects. There are, in fact, few which are 

 dopendcnt on a single species for pollination, and, so far as I know, 

 our yuccas furnish the only instance of this kind. It is to the fertili- 

 zation of these plants that I would first draw your attention. 

 The Yuccas (Fig. 57) are a characteristic American group of lilia(^eous 



Fig. 57. — Flower of Tucca aloifolia fully opened. 



plants, finding their home more particularly in the southern United 

 States and Mexico. There are many species which have been divided 

 even into subgenera by Dr. Engelmann, as Sarcoj-ucca, Clistoyucca, 

 Chenoyucca, and Hesperoyucca ; but for our present purpose they may 

 all be included under the one g^nus Yucca, as they all possess certain 

 characteristics in common, viz, a thick, submucilaginous root, which is in 

 reality a subterranean stem; lance-shaped, evergreen leaves, narrow or 

 broad, rigid or flaccid, and with the edge either filamentose, smooth, or 

 more or less distinctly serrate. The leaves produce a coarse fiber, val- 

 uable for certain kinds of fabrics, while the trunks of the tree Yuccas 

 have been used to make the toughest kind of paper. The fruit of some 

 species, as of aloifolia and haccaia, is fleshy and edible. It is, however, 

 the flowers to which I would draw more especial attention. They are 

 produced in largo panicles, and are characterized, as a rule, by the 

 anthers not reaching anywhere near the stigma, so that fertilization 

 unaided can take place only by the more.><t accident. The Yuccas sliow 

 great variation in detail, both in leaf, general habitus, flower-stalk, flower 



