1888.] NATURAL SCIENCES OF PHILADELPHIA. 398 



difficulty in perceiving in these elms and maples in the spring of 

 1887, that the pollen had been dispersed weeks before the pistil was 

 mature. The past season (1888) examination showed the anthers 

 bursting simultaneously with the receptive conditions. There was 

 an abundant crop of seeds. The maple is usually inclined to dioecism. 

 Although the flowers may seem perfect, the stamens in some fertile 

 flowers never proceed beyond anthers that give no pollen, while in 

 other cases perfect stamens with filaments and fertile anthers are 

 produced, Avhen the gynoecium seems unable to fulfil its functions. 

 But the elm, at least here, seems a full hermaphrodite, yet only this 

 season of three successive ones, had it full hermaphrodite functions. 

 In the two first it was so very proterandrous as to be barren. It 

 was not proterandrous this year, though I cannot say it was pro- 

 terogynous. It was, in fact as Avell as in name, hermaphrodite. 



Surely I am warranted in presenting the formula, that varying 

 measures of temperature variously affect the separate sexual organs, 

 and that the dichogamy has its origin in this simple circumstance. 



It is interesting to note how near we may get to a great truth 

 without actually perceiving it till long afterwards. In 1868, I 

 announced, through the Proceedings of the Academy, my discovery 

 that Mltchella repens was not merely heterostyled but practically 

 dioecious. I had subsequently found a white-berried variety which 

 bore berries freely when surrounded by its companions, but I never 

 had one during the many years it was under culture in my 

 garden. Up to that time and subsequently, the course of these 

 phenomena was obscure. Mr. Darwin, in Forms of Floivers (Chap. 

 A"II), observes : " But according to Mr. Meehan Mltchella itself is 

 dioecious in some districts. * * ^ Should these statements be 

 confirmed, Mitchella will be proved to be heterostyled in one district 

 and dioecious in another." With our present light we can readily 

 see how this may easily be. 



Now what is the significance of dichogamy ? The general view at 

 the present time is substantially the same as given in the work 

 above quoted. There Darwin expresses it in these words : " Va- 

 rious hermaphrodite plants have become heterostyled, and now ex- 

 ist under two or three forms ; and we may confidently believe that 

 this has been effected in order that cross-fertilization should be as- 

 sured." 



With the new light I have thrown on the origin of dichogamy, I 

 am sure the great Darwin would be ready to modify this view. It 

 cannot have the significance we all thought it had at that time. 



