144 THE ORIGIN OF SPECIES 



have their organs of fructification closely inclosed, as In 

 the great papilionaceous or pea-family; but these almost 

 invariably present beautiful and curious adaptations in 

 relation to the visits of insects. So necessary are the 

 visits of bees to many papilionaceous flowers that their 

 fertility is greatly diminished 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's- 

 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 sup- 

 posed 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 invarial)ly 

 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 pos- 

 sible to raise pure seedlings, so largely do they naturally 

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

 being favored, there are special contrivances which 

 effectually prevent the stigma receiving pollen from its 





I 



