Of INDIVIDUALS. 85 



In the first place, I have collected so large a body of 

 facts, and made so many experiments, showing, in accord- 

 ance with the almost universal belief of breeders, that with 

 animals and plants a cross between different varieties, or 

 between individuals of the same variety but of another 

 strain, gives vigor and fertility to the offspring; and on the 

 other hand, that close interbreeding diminishes vigor and 

 fertility ; that these facts alone incline me to believe that it 

 is a general law of nature that no organic being fertilizes 

 itself for a perpetuity of generations ; but that a cross with 

 another individual is occasionally — perhaps at long intervals 

 of time — indispensable. 



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

 understand several large classes of facts, such as the follow- 

 ing, which on any other view are inexplicable. Every 

 hybridizer knows how unfavorable 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 

 enclosed, as in the great papilionaceous or pea-family ; but 

 these almost invariably present beautiful and curious adapta- 

 tions 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-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-f ertilization j 



