FURTHER STUDIES OF YUCCAS. 219 



All of the Yuccas agree in the possession of a general 

 liliaceous type of flower, and in having compound pistils 

 with a stylar canal and septal nectar glands. The latter 

 characters, however, pertain to a considerable group of 

 Monocotyledons, and evidently antedate the evolution of the 

 Liliaceae as an order.* If my view is correct, each of these 

 characters came to Yucca in a fairly advanced state of 

 development, from an earlier type of monocotyledonous 

 plants. In brevi 'folia or its immediate ancestors, as well 

 as in the eastern Yuccas, the stylar canal appears to have 

 been extended and amplified at top through the marginal 

 union of erect stigmatic lobes, so as to form the peculiar 

 stigmatic chamber into which the pollen must be thrust 

 in order to properly develop its tubes and fertilize the 

 ovules. 



Originally having spreading stigmas, we may assume that 

 the progenitors of the Yuccas were slightly specialized ento- 

 mophilous flowers, pollinated by hymcnoptera, diptera or 

 lepidoptera, which were attracted by the secretion of the 

 septal nectar glands. With the consolidation of the stigmas, 

 however, insects visiting the flowers for this nectar became 

 inefficient pollinators, as may be seen when such insects 

 enter the flowers of the existing Yuccas for the little 

 nectar still produced ; hence, with an economic reduction 

 of the secretion of these glands, may have come an addi- 

 tion of their function to that normally borne by the stigma, 

 in an increase in its secretion, so that the visitors, laden 

 with pollen unconsciously accumulated while in the flower, 

 should further visit the stigma on which some of their 

 burden might be rubbed while they were feeding. Dur- 

 ing this stage of its evolution the plant appears to have 

 proved especially attractive to some small moth, perhaps 



* For a stylar canal in Agave see Danielli. Studi sulP Agave Ameri- 

 cana, Florence, 1885, 59, pi. 10; George and Wittmack, Gartenflora, 1892, 

 273, f. 55, but incomplete. References to the principal papers on septal 

 nectar glands are given in a short note by myself in the Bulletin of the 

 Torrey Botanieal Club, 1886, 135. 



