Chap. IV. OF INTERCROSSING. 97 



these facts alone incline me to believe that it is a 

 general law of nature (utterly ignorant though we be 

 of the meaning of the law) that no organic being self- 

 fertilises itself for an eternity of generations ; but that a 

 cross with another individual is occasionally — perhaps 

 at very long intervals — indispensable. 



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

 think, understand several large classes of facts, such as 

 the following, which on any other view are inexplicable. 

 Every hybridizer knows how unfavourable exposure to 

 wet is to the fertilisation of a flower, yet what a multi- 

 tude of flowers have their anthers and stigmas fully 

 exposed to the weather! but if an occasional cross be 

 indispensable, the fullest freedom for the entrance of 

 pollen from another individual will explain this state 

 of exposure, more especially as the plant's own anthers 

 and pistil generally stand so close together that self- 

 fertilisation seems almost inevitable. Many flowers, on 

 the other hand, have their organs of fructification closely 

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

 but in several, perhaps in all, such flowers, there is a 

 very curious adaptation between the structure of the 

 flower and the manner in which bees suck the nectar ; 

 for, in doing this, they either push the flower's own pollen 

 on the stigma, or bring pollen from another flower. So 

 necessary are the visits of bees to papilionaceous flowers, 

 that I have found, by experiments published elsewhere, 

 that their fertility is greatly diminished if these visits 

 be prevented. Now, it is scarcely possible that bees 

 should fly from flower to flower, and not carry pollen 

 from one to the other, to the great good, as I believe, 

 of the plant. Bees will act like a camel-hair pencil, 

 and it is quite sufficient just to touch the anthers of 

 one flower and then the stigma of another with the 

 same brush to ensure fertilisation ; but it must not be 



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