FURTHER STUDIES OF YUCCAS. 197 



in quiet weather, and especially at night, when the wind 

 sometimes falls ; and the development of the stigma two 

 days in advance of the stamens of a given flower, renders 

 close fertilization in the strictest sense improbable. 



The light yellow pollen is in such marked contrast with 

 the smoky tint of the moth, that laden females are recog- 

 nizable from a considerable distance, and notwithstanding 

 the failure of direct observation, there is every reason to 

 believe that the latter collect their burden from the older 

 flowers with the same deliberateness that has been observed 

 in the other known species of Pronuba, since it is held 

 under the well developed tentacles in the same manner as 

 by them. 



On first examining the flower clusters of brevifolia, I 

 was impressed by the remarkable symmetry of most of the 

 fertilized pistils, some of which had already reached half 

 the size of the mature fruit, which is in marked contrast 

 with the constriction or indentation of the eastern capsular 

 Yuccas at the point where the ovary has been punctured in 

 oviposition. This absence of deformity was explained, 

 however, when the act of oviposition was witnessed, for 

 the moth pierces, in this species, the uppermost pail of the 

 style, conveying its eggs down to the ovary through the 

 stylar channel, — the course followed by the pollen tubes. 



The female of most species of Pronuba seeks for a fresh 

 flower in which to deposit her eggs, showing preference for 

 one in the first night of expansion. To this she is probably 

 impelled by the impulse to insure for her offspring a suf- 

 ficient supply of food, the younger flowers being less likely 

 than the older to be already overstocked with eggs. This 

 instinct is particularly marked in P. synthetica, which I 

 have never seen ovipositing in any but the youngest flowers, 

 while I have repeatedly seen the pollen-laden moths force 

 themselves into the very narrow clefts between the rigid 

 sepals of an opening bud, their flattened form facilitating 

 this, after which only the most fragmentary glimpses of 

 their work were possible. But during something over a 



