196 



Introduction to Botany. 



141. Cross Pollination of Yucca. Thus far we have taken 

 for our illustrations flowers which 

 are more or less profoundly modi- 

 fied to secure cross pollination as 

 a necessary incident attending 

 the visits of insects. We shall 

 now examine an instance of quite 

 another character, and in some 

 respects even more wonderful 

 ^^^_ than those which have been 



FIG. 112. described. The flowers of the 



Photograph of a honey bee that has genus Yucca, representatives of 



died from exhaustion in its efforts . 



to free itself after its legs had been which are commonly found in 



gardens, depend almost entirely 

 upon the Pronuba moth for their 

 pollination. The structure of the flower is very simple and 

 readily understood. The 

 perianth is of the lilia- 

 ceous type, there being 

 three sepals and three pet- 

 als, all of a creamy white 

 color. In some of the 

 Yuccas these droop for- 

 ward and form bell-shaped 

 flowers, while in others 

 they are more widely 



Spreading. The Six Sta- Photomicrograph of a pair of pollinia of As- 



mens Consist Of fleshy, cle P ias cornuti attached to their corpuscu- 



. lum, as they appear when withdrawn from 



OUtward-CUrving filaments their pollen sacs. Photographed by trans- 

 mitted light, and on account of the opacity 

 of the corpusculum the slit in it is not shown, 

 but a portion of a leg of a small insect is 

 pendent from the slit. The pollen grains 

 of which the pollinia are composed can be 

 made out. X 15. 



surmounted by small an- 

 thers. The pistil extends 

 beyond the stamens, and 

 the three carpels are im- 



