FURTHER STUDIES OF YUCCAS AND THEIR POLLINATION. 



BY WILLIAM TRELEASE. 



Among the many strange things brought to light by 

 biological studies, few equal in interest or verge so closely on 

 the improbable as those which concern the pollination of 

 the Yuccas. The observed facts, chiefly known through 

 the work of Professor Charles V. Riley and the late Dr. 

 George Engelmann, have been admirably summarized by 

 Professor Riley in the Third Report of the Garden.* So 

 far as direct observation on pollination is concerned, these 

 refer to cultivated specimens of Y. filamentosa and glauca, 

 the latter of which has been observed also in the wild 

 state in Colorado ; f but the collections of entomolo- 

 gists, and the affected fruits of the Yuccas of various 

 localities, show that virtually all species of the genus 

 depend for their principal pollination, if not altogether, 

 upon moths of the Tineid genus Pronuba, of which Riley 

 has characterized three species, i Professor Riley, there- 

 fore, states that all of the species of Yucca native east of 

 the Rocky Mountains depend for their pollination, so far 

 as is now known, upon a single species of Pronuba, namely 

 the white P. yuccasella , while the tree Yucca of the 

 California desert and the adjacent region, Y. brevifolia, 

 is pollinated by a dingy moth, P. synthetical and the 

 aberrant Yucca W7iipplei, which Mr. Baker is now dis- 

 posed to place in a distinct genus under the name Hespero- 

 yucca, is pollinated by an equally aberrant spotted moth, 

 P. maculata^ the pollinating actions of which have been 

 briefly reported this season by Coquillet. * * Aside from this 



* pp. 99 to 158, pi. 34 to 43. f Riley, I. c. 124. J I. c. 137. 



I. c. 104, 121; Proc. Biological Society of Washington, vii. 94; 

 Insect Life, iv. 369. || I. c. 121, 141. f ?. c, 121, 139. 



** Insect Life, iv. 370, note. 



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