FURTHER STUDIES OF YUCCAS. 201 



]ike that of certain forms of filamentosa, involving, as it 

 appears to do, a loss of the services of Pronuba and conse- 

 quent sterility in all but exceptional cases of early blooming, 

 is especially worthy of study, considering the usual close 

 correspondence of the period of blooming of the Yuccas 

 with that of the appearance in the perfect form of their 

 Pronubas. 



c. CHiENOYUCCA, with dry, septicidally dehiscent capsules. 



Y. rupicola, Scheele. — No observations have been re- 

 corded on the pollination of this Texan species, which 

 Professor Riley* believes may have a distinct Pronuba. It 

 is not uncommon from Fort Worth southward, on the 

 black soil with intermingled limestone, but I failed to study 

 wild plants. At Dallas, however, through the kindness of 

 Mr. J. Reverchon, I was able to examine specimens culti- 

 vated on his place, which were blooming simultaneously 

 with the wild Y. glauca, var. stricta and frequented 

 by Pronuba yuccasella like the latter. These plants are 

 abundantly fertile (each crown dying after blooming), and 

 the structure of the flower indicates that the moth works 

 on them as she does on the filamenlosa group, though I 

 was unable to observe her actions. Their seedlings are 

 now spontaneous about the place, and so variable that Mr. 

 Reverchon suspects hybridization with the native variety of 

 glauca, as well as cultivated forms of filamentosa. This 

 will prove an interesting subject for future study, since the 

 habits of Pronuba in caring for her young are so highly 

 specialized, and the details are so minutely carried out, that 

 it was hardly to be expected that a given individual would 

 indiscriminately pass from one species of Yucca to another, 

 though on the other hand, it is known that the more eastern 

 species are all pollinated by representatives of the single 

 species of Pronuba. 



Y. elata, Engelm. (PL 10, 15, 22). — Beginning in west- 

 ern Texas, about the limits of glauca, this Yucca gradually 



* I. c. 122. 



