120 ON THE INTERCROSSING [Chap. IV. 



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 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-fertili- 

 sation, the fullest freedom for the entrance of pollen from 

 another individual will explain the above state of expo- 

 sure 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 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- 

 hair pencil, and it is sufficient, to ensure fertilisation, 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 com- 

 pletely destroys, as has been shown by Gartner, the 

 influence of the foreign pollen. 



When the stamens of a flower suddenly spring towards 

 the pistil, or slowly move one after the other towards 

 it, the contrivance seems adapted solely to ensure self- 



