OBSERVATIONS OX Fl^OWEEING PERIODS OF CERT.VIN CACTI. 33 



ill the view that the flowering period of cacti is determined by the 

 advent of the rain.^ 



Perhaps a less dogmatic way to put it is to say that there is 

 as yet a very insufficient basis for such a generalization, and the 

 whole question becomes an open one. The truth of this is fur- 

 ther indicated by the fact that in many cacti the flowering com- 

 mences long before the turgid condition, following the advent of 

 the rain, has been assumed. For instance, I have noted certain 

 of the arborescent opuntias, notably O'fn.intia fulgida, producing 

 flowers in abundance, while the ultimate articles from which they 

 sprang, as indeed the whole plant, w^ere in a woefully shriveled 

 condition. 



And from this we might be further led to conclude that the 

 process does not depend on an optimum or even a moderate 

 abundance of water in the plants themselves, a conclusion obvi- 

 ously open, in many cases, to much doubt. Some of the species 

 of MamiUaria appear to wait till the rains come. It is clear 

 that the water supply of cactus flowers is derived, in many cases, 

 entirely from the plant. It is a common sight to see a cactus 

 (e. g. Echinocachis wislczeni) flowering abundantly after be- 

 ing uprooted for at least six months. It serves nevertheless to 

 ■direct our attention to the fact that here is a definite problem not 

 yet begun to be settled, and about which it is very unsafe to make 

 generalizations at too great a distance. That the flowers as such 

 ai-e not, at least in a striking way, adapted to withstand the ad- 

 verse conditions of low relative humidity, appears to be probable, 

 as they are, as a class, ephemeral. The exceptions to this rule 

 are to be found in such species as the saguaro, Cereus giganteus, 

 the flower of which is said to open on the second day, a point 

 which I regret not to have settled beyond doubt for myself. I 

 do know, however, that the flowers of a closely related species, 

 Cereus Tliurheri, the pitalla, in which the anatomical and gross 

 ■characters of the flower are very closely comparable, if not prac- 

 tically identical, with those of the flower of Cereus giganteus, 



1. Ganong, W. F. Present problems in the anatomy, morphology and 

 biology of the Cactaceae. Bot. Gaz. 20: 129, 1895. 



