222 MISSOURI BOTANICAL GARDEN. 



acquiring their more general adaptations because of separa- 

 tion from Prodoxids, and readjusting themselves to their 

 former pollinators on again coming within their reach ; and 

 I am disposed to think that this is the case, rather than to 

 assume that the generalization antedates their first asso- 

 ciation with Pronuba. 



The evolution of the Pronubas has presumably gone hand 

 in hand with the adaptation of the Yuccas to their services 

 in pollination, and has been sketched, in its essential feat- 

 ures, by Professor Riley. It is interesting to observe that 

 one species, P. yuccasella, accompanies the true Yuccas of 

 the most differentiated type across the continent from the 

 south Atlantic states to southern California (and undoubt- 

 edly the peninsula), and that, as the pollinator of Y. baccata, 

 it occurs in California associated with P. synlhetica and P. 

 maculata and its curious black derivative, which pollinate 

 respectively the archetypal Y. brevifolia and the greatly 

 differentiated Hesperoyuccas, thus strengthening the in- 

 ference that the latter two are primarily Pacific tj'pes, while 

 baccata in its present form is an immigrant from the East, 

 which has been accompanied by the common pollinator of 

 the eastern species. 



In a paper read before the American Association for the 

 Advancement of Science at Rochester, in August, 1892, 

 Professor Smith has shown that the curious tentacles used 

 by the moth in pollinating the Yucca flowers, occupy a 

 position similar to that of the palpif er on the maxillro of 

 other groups of insects, and so is disposed to homologize 

 them with those parts. As Professor Cope has suggested 

 to me, a fuller knowledge of the embryology of lepidoptera 

 may show the general prevalence of similarly situated 

 processes in the early differentiation of the maxillae, and 

 thus remove the only valid objection that I see to Professor 

 Smith's conclusions, the isolated occurrence of these 

 appendages in the group of lepidoptera. At present they 

 are known in a developed form only on the females of 

 Pronuba, and as rudiments on the males of that genus and 



