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 MVasure tells us in the most emphatic manner 
that she abhors perpetual self-fertilization. Darwin found here, therefore, confirmation 
of the conclusion stated by him as a general law in his work on the Origin of 
Species—LVo organic being can fertilize itself through an unlimited number of genera- 
tions ; but a cross with other individuals rs occastonally—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 Polygala, Salvia, Aristolochia, and others; to Buchenau 
on Pinguicula, Utricularia, Aspidistra; to Fritz Miiller on Martha; to Engler 
on Saxtfraga. 
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, Spiranthes), 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 :—(1) 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 Aurivillius that the 
flowers of Pedicularis lanata (and hirsuta) 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. 
? Asa Gray was born on November 18, 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, 1888. 
’ For the following statement I am indebted to Professor F. Ludwig, of Greiz. Fritz Miiller, 
