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THE POPULAR SCIENCE MONTHLY. 



yucca fertilization was for many-years a vexed question ; Engel- 

 mann spent much thought and observation in trying to learn its 

 secret, and finally, over twenty years ago, called the attention of 

 Prof. C. V. Riley, the noted entomologist, to certain moths which 

 frequented the yucca flowers. After long and patient study and 

 various erroneous speculations the two scientists ultimately 

 brought the whole mystery to light ; and in a recent paper, pub- 

 lished in the Report of the Missouri Garden for 1892, Riley has 

 fully elaborated his work of the earlier years and the observations 

 made in the intervening time. The structure of the yucca flower 



Fio. 9. — Yucca aloifolia. 



is plainly outlined in Fig. 10. Long experimentation has positively 

 shown that it is practically impossible for the sticky pollen to be 

 transferred from the little anthers on the tips of the short stamens 

 to the fine stigmatic tube opening only at the tip of the pistil, except 

 by external voluntary agency. As a matter of fact, the agency is 



