" (5/12. 'Nature' October 10,
1872 page 479. Hermann Muller gives an elaborate description of the
flowers 'Befruchtung' etc. page 247.) Notwithstanding these manifest
provisions for cross-fertilisation, varieties which have been cultivated
for very many successive generations in close proximity, although
flowering at the same time, remain pure. I have elsewhere given evidence
on this head, and if required could give more. (5/13. 'Variation of
Animals and Plants under Domestication' chapter 9 2nd edition volume 1
page 348.) There can hardly be a doubt that some of Knight's varieties,
which were originally produced by an artificial cross and were very
vigorous, lasted for at least sixty years, and during all these years
were self-fertilised; for had it been otherwise, they would not have
kept true, as the several varieties are generally grown near together.
Most of the varieties, however, endure for a shorter period; and this
may be in part due to their weakness of constitution from long-continued
self-fertilisation.
It is remarkable, considering that the flowers secrete much nectar and
afford much pollen, how seldom they are visited by insects either in
England, or, as H. Muller remarks, in North Germany. I have observed the
flowers for the last thirty years, and in all this time have only thrice
seen bees of the proper kind at work (one of them being Bombus
muscorum), such as were sufficiently powerful to depress the keel, so as
to get the undersides of their bodies dusted with pollen.
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