I shall hereafter have occasion to show that the
exotic Lobelia fulgens, in this part of England, is never visited by
insects, and consequently, from its peculiar structure, never can set
a seed. Many of our orchidaceous plants absolutely require the visits
of moths to remove their pollen-masses and thus to fertilise them. I
have, also, reason to believe that humble-bees are indispensable to
the fertilisation of the heartsease (Viola tricolor), for other bees
do not visit this flower. From experiments which I have tried, I have
found that the visits of bees, if not indispensable, are at least
highly beneficial to the fertilisation of our clovers; but humble-bees
alone visit the common red clover (Trifolium pratense), as other bees
cannot reach the nectar. Hence I have very little doubt, that if the
whole genus of humble-bees became extinct or very rare in England, the
heartsease and red clover would become very rare, or wholly disappear.
The number of humble-bees in any district depends in a great degree on
the number of field-mice, which destroy their combs and nests; and Mr.
H. Newman, who has long attended to the habits of humble-bees,
believes that "more than two thirds of them are thus destroyed all
over England." Now the number of mice is largely dependent, as every
one knows, on the number of cats; and Mr. Newman says, "Near villages
and small towns I have found the nests of humble-bees more numerous
than elsewhere, which I attribute to the number of cats that destroy
the mice.
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