34 THE PLAINT WORLD. 



are ephemeral, and in fact open only at night, and not in the day 

 time at all. I observed this while on a visit to the Quiqotoa Moun- 

 tains, ninety miles west of Tucson, where is to he found a limited 

 and isolated station, but where it grows abundantly and luxuri- 

 ously on the western slope of the mountains. I found it to be 

 a true night-blooming cereus, opening at sunset, and occupying, 

 in the process, a half to one hour. It is a very singular fact, that 

 of two closely related species, the flowers of which are so much 

 alike in all points of structure, and, if adapted to insect or other 

 visitors at all, to the same kinds, the diurnal flowering period 

 should fall, in one species in the day time, and in the other at 

 night. The same insect visitors may indeed be useful at both 

 times, as is true to my knowledge in the cases of Opuntia fulgida, 

 the flowers of which are abundantly visited, in light and dark 

 alike, by the little grey beetle, Bruchus amicus, kindly identified 

 for me by Dr. L. O. Howard, of the U. S. Department of Agri- 

 culture. So that this point may present no difiiculties, since 

 there is no need to assume that night and day flowers are polli- 

 nated by different kinds of visitors, although it may be true in 

 particular instances, even when the flowers are as much alike in 

 form as in the two species above referred to. The more diflicult 

 part of the problem lies in the practical structural identity of 

 the two flowers of the two species. We have generally supposed 

 the flowers of the night bloomers to be of a delicate nature. Cer- 

 tainly the majority have a more evanescent appearance, an im- 

 pression which one gets on looking, as I did for the first time last 

 year, on the singularly tender flowers of Cereus greggii, which 

 set out its amiual arrav for us this year on the 11th of Julv-^ 

 And so also with others which are more familiar to us through 

 cultivation or otherwise. But the flowers of Cereus iliurheri, 

 are, in appearance, of no such ethereal nature. And yet the sun 

 never looks upon them, while the ghostly petals of Cereus greggii 



1. The date of flowering in 1903 was June 21. Of this plant Englemann 

 remarked, "They seem to be mostly nocturnal, as Mr. Thurber collected them 

 in the early morning hours, commencing to fade" (Cactaceae of the U. S. and 

 Mex. Bound. S. p. 41). What is more, almost all the flowers open in a single 

 night of the year. 



