196 MISSOURI BOTANICAL GARDEN. 



of the ovary. Externally they open in the usual manner , 

 but the deep outer septal grooves are little if at all expanded 

 into a conducting channel, though they reach to the base 

 of the pistil in the usual manner and expand there into 

 triangular spaces. I have not observed any evidence that 

 the septal glands secrete at all, nor is the stigmatic secretion 

 as abundant here as in most species. 



The dark colored Pronuba synthetica, which Professor 

 Kiley * describes as peculiar to this Yucca, rests during the 

 day within the flowers in much the position already de- 

 scribed for the eastern P. yuccasella, or, especially when 

 disturbed, retires between the densely crowded flowers, 

 where it is protected from most dangers ; but it is more 

 active through the day than its eastern congener. Towards 

 evening the moths become quite active, and it is probable 

 that copulation of the sexes occurs before night, for I have 

 not seen male moths at night within the flowers where the 

 females were occupied in oviposition. There is also reason 

 to believe that the latter accumulate their loads of pollen at 

 an early hour, though this again is only inference, since I 

 have not witnessed the operation, even in the cases in 

 which I have suspected that a moth was so employed, owing 

 to the peculiarly closed condition of the flowers. Unlike 

 the other known species, this Pronuba appears slow to take 

 flight. Though it is easily disturbed, so as to run about 

 and seek concealment between the flowers, I have seen it 

 take to the wing only a few times, and then it merely sailed 

 down to the ground, not far from the tree. This apparent 

 indisposition to leave the flowers may, perhaps, be con- 

 nected with the almost constant occurrence of high winds 

 on the desert. Whatever its cause, this habit of the moths 

 appears to. restrict cross-pollination to flowers of the same 

 plant more closely than is the case with other Yuccas, 

 though there must be frequent flights from plant to plant 



* 1. c. 121, 141; Proc. Biol. Soc. Washington, vii. 94; Insect Life, iv. 

 370. (This was first called P. paradoxa, but without description. Riley 

 Proc. Wash. Ent. Soc. 1888, i. 154, and Insect Life, i. 372. 



