FERTILIZATION OF FLOWERS BY INSECTS. 273 
accomplishment of this transfer, when it would have been much 
more simple to dispose the organs in such a way that the anthers 
might cast the pollen immediately upon the stigmas? The reason 
of this Sprengel failed to comprehend, nor should we be more 
successful without recognizing an important natural law recently 
detected by the author of the doctrine of natural selection.* : 
Charles Darwin saw, what Sprengel failed to see, that the princi- 
pal effect of the action of insects upon plants is the transfer of 
the pollen of one individual to the stigma of another. To this 
conclusion he was led by his beautiful researches on the floral 
structure and the fecundation of Orchids. And from these he 
subsequently inferred that it is advantageous to every vegetable to 
have its pistils fecundated by the pollen of other individuals of the 
same species, rather than by its own. As soon as observation had 
made Darwin master of this great truth, he resorted to the control 
of experiment. The experiments made by him with unwearied 
diligence through a long series of years— scattering upon the 
stigmas of plants of the same species, sometimes their own pollen, 
sometimes that of others—placed it out of doubt that the impol- 
lination of the stigmas with the pollen of other individuals, or the 
intercourse between distinct individuals, produces an offspring more 
numerous, more robust, and capable of greater development than if 
Jecundation had been produced by its own pollen; a thesis which 
subsequently became amply confirmed by the numerous a 
ments of Hildebrand, my brother Fritz, and others. The enigma 
of floral structure is then solved, and we will now pass to the 
*The author e to Charles Darwin the merit of having mio formulated the 
law of 2 necessity of cross-fertilization even for hermaphrodites; but this law, al- 
ready partially seen a Keelreuter, was comprehended in nearly all its vigor by C. C 
Spreng 
"Reuter having i in 1761 made tho apa that in the page e Gone and ikse 
anthers, and the 
uae with pollen from other flowers, makes pen following Aioni iin esis ss re id 
aliquid in proprio suo pulvere sed 
semper eo aliorum suz speciei impregnentur, merito queritur. Certe natura nil facit 
frustra.” 
C. C. Sp: ent further, and on p. 43 of his bii “Das entdeckte Geheimniss 
der Natur i in Doa a und in der Befruchtung der Blumen ” (1793) uses these memorable 
words: “ Since there are so many unisexual flowers, and since among 
fl th 1 female organs at the same 
time, it appears that nature does not wish that each flower should fecundate with its 
pollen.” And h de by him upon the flowers 
of Hem ouie al aid. after being fecundated artificially with with their own pollen 
never perfected the seeds. 
