NATURAL SCIENCE 



A iMonthly Review of Scientific Progress. 



No. 15. Vol II. MAY. 1893. 



M 



NOTES AND COMMENTS. 



The Pollination of the Yucca. 



R. A. W. BENNETT, in his article in the March number of 

 Natural Science, refers to the polhnation of the Yucca, a well- 

 known liliaceous plant, by a moth {Pvonuha yuccasella), and those in- 

 terested in the subject will find some " Further Studies," by William 

 Trelease in the fourth annual report of the Missouri Botanical Garden. 

 Hitherto, only two species, Ji/amentosa and glanca, have been directly 

 observed under cultivation, and the latter wild in Colorado, and the 

 moth Pronuba is the pollinating agent in both. The present report 

 describes further investigations in the field on these and other species. 



The flowers of Yucca baccata, a widely distributed species, ranging 

 in a variety of forms from southern Colorado into Mexico and Cali- 

 fornia, are frequented by a moth somewhat larger and a little darker 

 in colour than the P. yuccasella of the Mississippi Valley and Rocky 

 Mountains, but otherwise indistinguishable from it, as is also the 

 moth of the Gulf region. Like the Eastern representative, it rests 

 withm the flower during the day with the head directed towards 

 the base of the stamens, and when depositing the egg, at night, 

 "doubtless backs down between the upper ends of the stamens," piercing 

 the ovary at about its middle in the thinnest part, viz., that between 

 the internal partitions, which is not covered by the lower part of the 

 stamen. " After thus depositing the egg in the ovule of the plant, the 

 females behave as in Y. filamentosa, carrying loads of pollen from the 

 anthers and thrusting it into the cavity of the stigma with the 

 proboscis. This open canal is frequented by numbers of a white 

 Thrips, which sometimes penetrate the cells of the ovary and doubt- 



