212 MISSOURI BOTANICAL GARDEN. 



fruit whatever was found except that Avhich clearly showed 

 the work of Pronuba. At best, therefore, I should say that 

 where its proper Pronuba is absent, Whipple* has only the 

 limited power of self-pollination, or pollination by other 

 agents, that is possessed by aloifolia among the true Yuc- 

 cas. I have also no evidence that pollen tubes overdevelop 

 in such a manner as to reach and fertilize the ovules 

 from pollinia placed on the margin of the stigma, although 

 search was made for something of the sort; and a deter- 

 mination of the extent to which fertilization in this manner 

 is possible must be made by a series of experiments such as 

 I could not carry out in the time at my disposal.* 



The characters of Pronuba rnaculata have been so fullv 

 given by Riley that nothing need be added to his descrip- 

 tion. From the frequently open character of the flowers, 

 and, especially, the withdrawal of the stamens from the 

 pistil, these moths are, however, constrained to behave 

 quite differently from the other species of their genus; and 

 very probably in connection with the more diurnal nature 

 of the Hesperoyucca flowers, they are far more active in 

 the day time than their congeners are. Unless locally ab- 

 sent, they are readily observed whenever the flowers are 

 examined, either resting in them or engaged in pollination 

 or oviposition, and at first sight it is difficult to say whether 

 they are quiescent or engaged in the latter operation, for, 

 unlike the other known Pronubas, they rest with the head 

 toward the stigma, usually standing upon the side of the 

 ovary, — a position almost identical with that taken in ovi- 



* Since the above was written, Professor Riley, under date of October 

 13, 1892, writes me that in a manuscript report on the pollination of 

 Whipplei, Mr. Coquillet of Los Angeles records the seeding this year of a 

 number of pods or panicles which he had covered with gauze before any of 

 the flowers opened. Professor Keruer von Marilaun (Pflanzenleben, ii. 

 155, figures 1 to 5), states that in repeated cases of blooming in the 

 Vienna Garden this species has never matured its fruit. The figures 

 which accompany his account of Yucca pollination represent some Eu- 

 yucca, — apparently a form of ftlamentosa, — though they bear the name 

 Whipplei ; and the moth represented as pollinating the flower (adapted by 

 the artist from Riley's figures), is yuccasella. 



