120 ON THE INTBRCEOSSING. [Chap. IV, 



On ths belief that this is a law of nature, we can. 

 think, understand several large classes of facts, such a 

 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 ex< 

 posed to the weather ! If an occasional cross be indis- 

 pensable, notwithstanding that the plant's own anthers 

 and pistil stand so near each other as almost to insure 

 self -fertilisation, 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 almost invariably present beautiful and curious 

 adaptations in relation to the visits of insects'. So neces« 

 sary 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 an- 

 thers 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 to- 

 wards the pistil, or slowly move one after the other to- 

 wards it, the contrivance seems adapted solely to ensure 



