90 Riley Some Interrelations of Plants and Insects. 



just mentioned. Sometimes two or more adjacent ovules are 

 thus affected." 



It may be well right here to look a little more closely into 

 the minuter characteristics of the Yucca flower at this stage of 

 its development that we may understand more fully the action 

 and influence of the moth. In my first article, published some 

 twenty years ago, announcing the discovery of Pronuba and its 

 action on Yucca pollination, I was strongly inclined to the idea 

 that the act of pollination had some compensating inducement 

 to the moth, aside from the impelling instinct of perpetuation of 

 the species. At that time it was supposed that the stigmatic 

 liquor was nectarian, and the conclusion was justifiable that the 

 moth, attracted to it for feeding purposes, would incidentally 

 induce pollination. On this view of the matter it did not require 

 a great stretch of the imagination to conceive that the pollen 

 might also incidentally accumulate in the spines, and that the 

 vigorous action of the head that had been noticed might even 

 be considered as an effort to get rid of the encumbrance while 

 feeding. In those days I was more imbued with the common 

 notion that lower creatures are impelled for the most part un- 

 consciously to their acts. Twenty years of study and experience 

 have only served to prove the acts of Pronuba the more unselfish 

 and without food inducement. A longitudinal section of the 

 upper portion of the pistil will show the style with the stig- 

 matic tube, which at this time communicates with the ovarian 

 cells. Now, Trelease has shown that the stigmatic liquor is not 

 nectarian, but that the slight amount of nectar associated with 

 the flower is secreted in pockets formed by the partitions that 

 separate the three cells of the pistil, and which open externally 

 near the style by a contracted pore from which the nectar is 

 poured through a capillary tube to the base of the pistil. The 

 accompanying illustration (Fig. 6) renders this more intelligible, 

 a being a longitudinal section through the center of a pistil, 

 showing the septal gland (</), the duct (d), and the outlet at 

 base ; 6, a cross-section of the pistil about the middle, also show- 

 ing the duct (d) and gland (#) ; c. a more enlarged cross-section 

 of the nectar apparatus ; e showing more fully the structure of 

 the septal gland, while h is a longitudinal section of the top of 

 the pistil, through the lobes, showing how the stigmatic tube O) 

 connects with the ovarian cell (o c), o being the ovary,./' the fu- 

 niculus, p the placenta, and/r fibro-vascular tissue. 



