NATURAL SELECTION 77 



On the belief that this is a law of nature, we can, I think, under- 

 stand several large classes of facts, such as the following, which on 

 any other view are inexplicable. Every hybridizer knows how un- 

 favorable exposure to wet is to the fertilization of a flower, yet 

 what a multitude of flowers have their anthers and stigmas fully 

 exposed to the weather! If an occasional cross be indispensable, 

 notwithstanding that the plant's own anthers and pistil stand so 

 near each other as almost to insure self-fertilization, the fullest 

 freedom for the entrance of pollen from another individual will 

 explain the above state of exposure of the organs. Many flowers, 

 on the other hand, have their organs of fructification closely en- 

 closed, as in the great papilionaceous or pea- family; but these al- 

 most invariably present beautiful and curious adaptations in rela- 

 tion to the visits of insects. So necessary are the visits of bees to 

 many papilionaceous flowers, that their fertility is greatly dimin- 

 ished if these visits be prevented. Now, it is scarcely possible for 

 insects to fly from flower to flower, and not to carry pollen from 

 one to the other, to the great good of the plant. Insects act like a 

 camel-hair pencil, and it is sufficient, to insure fertilization, just to 

 touch with the same brush the anthers of one flower and then the 

 stigma of another; but it must not be supposed that bees would 

 thus produce a multitude of hybrids between distinct species; for 

 if a plant's own pollen and that from another species are placed on 

 the same stigma, the former is so prepotent that it invariably and 

 completely destroys, as has been shown by Gartner, the influence 

 of the foreign pollen. 



When the stamens of a flower suddenly spring toward the pistil, 

 or slowly move one after the other toward it, the contrivance seems 

 adapted solely to insure self-fertilization; and no doubt it is useful 

 for this end: but the agency of insects is often required to cause 

 the stamens to spring forward, as Kolreuter has shown to be the 

 case with the barberry; and in this very genus, which seems to 

 have a special contrivance for self-fertilization, it is well known 

 that, if closely-allied forms or varieties are planted near each other, 

 it is hardly possible to raise pure seedlings, so largely do they natu- 

 rally cross. In numerous other cases, far from self-fertilization 

 being favored, there are special contrivances which effectually 

 prevent the stigma receiving pollen from its own flower, as I could 

 show from the works of Sprengel and others, as well as from my 

 own observations: for instance, in Lobelia fulgens, there is a really 

 beautiful and elaborate contrivance by which all the infinitely 

 numerous pollen-granules are swept out of the conjoined anthers 

 of each flower, before the stigma of that individual flower is ready 



