FURTHER STUDIES OF YUCCAS. 183 



bloomed for the first time in several seasons, and a number 

 of the panicles fruited quite freely. The earliest of these 

 flowers opened as the last flowers of Jilamentosa were fall- 

 ing, so that it was supposed at first that they were pollin- 

 ated by P. yuccasella, which had been observed only a few 

 days previously, but this supposition was not substantiated 

 by the discovery of the moth about them, or of its larvae in 

 the fruit. 



Professor Riley has shown that the short style and open 

 stigma of aloifolia appear to favor self-pollination when the 

 moth is not present ; but a study of our plants this summer 

 by Mr. Webber and myself has not satisfied either of us 

 that self pollination is likely to occur sufficiently frequently 

 to explain the rather abundant fruiting observed here, and 

 in the case of a single panicle covered with gauze, no fruit 

 was set except as the result of artificial pollination. The 

 so-called Yucca hybrids of gardens appear for the most 

 part if not always to be spontaneous or artificial crosses 

 between the variegated and other forms cultivated under 

 various names, but now generally referred to this species. 

 Altogether Y. aloifolia is one of the species most worthy 

 of study in its native habitat, since little is known except 

 that it sometimes fruits without the aid of Pronuba, and 

 that its seeds sometimes contain the larva? of P. yuccasella, 

 while the exact mode of pollination when the moth is 

 excluded is not known from observation. 



It is well known that Jilamentosa, when cultivated far 

 north of its range, is uncertain in its blooming, although 

 further south it flowers every year ; and attention has been 

 called frequently to the periodicity of brevifolia and other 

 species in their native home.* No doubt this is connected 

 with the previous conditions of nutrition, and the im- 

 mediate climatic influences under which the plants have 

 grown, but it appears quite remarkable that so many plants 

 of aloifolia at the Garden, of very different size and age, 



* Riley, I. c. 117. 



