32 THE PI.AXT WOELD. 



over ten years ago, and because, also, of tlie important physiolog- 

 ical problems they indicate. ISTo attempt has been made by me 

 to solve any of these experimentally on account of the preoccupa- 

 tion of my time, but to point out the field for work will not be 

 amiss. 



The annual flowering period for the cacti in the vicinity of 

 Tucson, Arizona, commences early in April at the close of the 

 winter rains, Cerciis fendlen being one of the first to put out its 

 marvelously beautiful flowers in abundant numbers. The sea- 

 son closes about the middle of September, when the last of the 

 flowers of the arborescent type of Opuntise, as e. g., the choUa 

 (0. fulgida) are to be seen. The beginning of the annual flow- 

 ering period of the species taken severally may occur at any time 

 between the inclusive dates given, save, of course, only the last 

 to commence, which will be several weeks before the last flower 

 is to be seen. The summer rains begin here about the middle of 

 July and continue, with abundant interruption, till the last of 

 September. This month, however, is not a wet one by any 

 stretch of the imagination, or at least, it was not this year, though 

 it will be understood the soil water is relatively abundant. 



It will then be seen that the flowering period of the cacti of 

 the region to which I refer falls, not at the end of the dry, nor at 

 the close of the rainy season, from which circumstance it is diffi- 

 cult to conclude that the production of flowers is in any way de- 

 pendent upon the abundance of water in the soil. This may be 

 the case with reference to particular species, but is to be proved. 

 But the fact that the latest species to flower conunence to do so 

 before the summer rains set in, early in July, appears to deny 

 this. Their flowering goes on without interruption during the 

 rains, but the maximum of flower production is not a striking 

 one, nor does it seem to be related to a greater aliundance of soil 

 water. That the flowers of cacti, then, are not adapted, as are 

 the plants from which they spring, to the dry conditions of the 

 desert, both above and below the surface of the ground, may in- 

 deed be true, but remains undemonstrated, and there is nothing 



