FURTHER STUDIES OF YUCCAS. 217 



under a cloudless sky, the first time at about noon. Flying 

 into a flower, the moth runs about the bases of the stamens 

 after the manner of other species, then quickly clambers 

 upon the inner side of a filament, and, with the tentacles 

 extended over the pollinia, drags first one and then the other 

 out of the anther cells, pressing them together under the 

 throat, and subsequently compacting the mass together 

 much as yuccasella docs the powdery pollen of other 

 Yuccas, so that the ball finally consists of as many as ten 

 or a dozen pollinia. So quick and energetic are the motions 

 by which the pollinia are removed, that the stamens are 

 often shaken quite violently, as I have before noted in the 

 more nervous attempts of yuccasella. Oviposition and 

 pollination, which were repeatedly witnessed, are performed 

 exactly as by the maculate moth, the very slow movement 

 in the latter operation being quite as striking. 



The relationship of the Yuccas to one another and to 

 their pollinators, the Pronuba moths, would be far more 

 intelligible if we could trace their history back even a short 

 distance into the later geological time, because as Yuccas 

 and Pronubas both are undoubtedly of recent origin ; but 

 as was pointed out in the Third Report of the Garden, this 

 is as yet impossible, since no certainly identifiable Yuccas 

 exist in even the latest deposits, though plants bearing 

 more or less resemblance to them occur far back in the 

 geological epoch. In his paper so frequently referred to in 

 the foregoing pages, Professor Riley has called attention 

 to the ancient type of vegetation represented by the tree 

 Yuccas. This is particularly true of Y. brevifolia, which 

 in aspect resembles restorations of the Carboniferous 

 Lepidodendron more nearly than any other form of recent 

 or fossil tree with which I am acquainted. The other 

 arboreous Yuccas are more like the Dracaenas in habit, but 

 the latter also belong to an antiquated type. 



Though no single species extends across the continent, 



