Chap. IV. 
OF INTEKCKOSSINa 
97 
fertility to the offspring; and on the other hand, that 
clo%e interbreeding diminishes vigour and fertility ; that 
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 fiowers, there is a 
very curious adaptation between the structure of the 
fiower 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 
