HISTORICAL DEVELOPMENT OF FLOWER POLLINATION 9 



significance of dimorphism appeared in 1862 (though the phenomenon had previously 

 been observed by Sprengel, and even before him by Curtis, about 1780, see footnote, 

 p. 45). In this work Darwin showed that the most abundant formation of seeds 

 takes place when there is pollination of the stigmas with pollen from stamens stand- 

 ing at the same level in other flowers (legitimate fertilization). In the same year 

 appeared his work on Orchids, in which he described the adaptations for fertilization 

 of British and foreign orchids in as instructive a way as Sprengel (whose book was 

 first again made mention of in this work, and so rescued from oblivion) had done 

 in the case of numerous other plants seventy years previously. These investigations 

 on orchids led to the conclusion that Nature tells us in the viost emphatic manner 

 that she abhors perpetual self-feriilizatio7i. Darwin found here, therefore, confirmation 

 of the conclusion stated by him as a general law in his work on the Origin of 

 Species No organic being can fertilize itself through an unlimited number of genera- 

 tions ; but a cross with other individuals is occasionally perhaps at very long intervals 

 indispensable ^ 



Although Darwin's first works on flower pollination were met with opposition, 

 even by prominent botanists like L. C. Treviranus and H. v. Mohl, yet they had in 

 a high degree a stimulating effect on numerous investigators, so that in the next few 

 years there were not only various supplementary works published by Darwin himself 

 (on Linum, Lythrum, Primula, &c.), but the science of flower pollination was added 

 to by others and especially by German botanists. Thus, in the sixties, Alefelt, 

 Hildebrand, Kuhn, Scott, and Walz worked at Heterostyly, while for descriptions 

 published during this decade on the flower pollination of definite species or groups of 

 plants we are indebted to Asa Gray, Anderson, Gosse, Scudder, Trimen, Weale, 

 Criiger, Scott, Moggridge, Hildebrand, Hermann Miiller, and Rohrbach on Orchids ; 

 to Robert Brown, Delpino, Hildebrand on Asclepiads and related forms; to Hilde- 

 brand who also worked on Poly gala, Salvia, Aristolochia, and others ; to Buchenau 

 on Pinguicula, Utricularia, Aspidistra; to Fritz Miiller on Martha; to Engler 

 on Saxifraga. 



In North America Asa Gray ^ after the appearance of Darwin's epoch-making 

 works, made investigation in flower pollination, especially in North American orchids 

 {Platanthera, Gymnadenia, Goodyera, Spiranihes), and subsequently on cleistogamy, 

 self-fertility, humming-bird-flowers, and other special floral adaptations (1862). 



In South America Fritz Miiller^ followed in the steps of Darwin, publishing 



* It may here be remarked that two more recent observations are opposed to this conclusion 

 with regard to the avoidance of self-fertilization, namely: (i) The flowers discovered by Burck of 

 species of the tropical genera Myrmecodia, Unona, Artobotrys, Goniothalamus, Cyathocalyx, always 

 remain completely closed. (2) The observation of Nathorst communicated by Anrivillius that the 

 flowers of Pedicularis lanata (and hirsutd) in Spitzbergen, where it is reported that there are no 

 humble-bees, produce fruit abundantly, and multiply by seeds, despite the fact that the anthers are 

 so completely enclosed by the upper lip that only humble-bees are able to put in motion the 

 mechanism of the flowers, and to effect a normal cross-fertilization. Accordingly it seems to be 

 established that in these two cases self-fertilization has taken place through many generations and 

 this without influence on the production of seed and the vitality of the offspring. 



2 Asa Gray was born on November 1 8, 1810, at Paris, in Oneida-County, in the State of New York. 

 He first studied Medicine, but subsequently devoted himself to Botany, and in 1842 became 

 Professor in Harvard College, Cambridge (Mass.). He died in this office on January 31, 188S. 



^ For the following statement I am indebted to Professor F. Ludwig, of Greiz. Fritz Miiller, 



