The
number of bees which frequent certain kinds of trees when in full flower
is very great, and they may be seen flying from tree to tree more
frequently than might have been expected. Nevertheless, if we consider
how numerous are the flowers, for instance, on a horse-chestnut or
lime-tree, an incomparably larger number of flowers must be fertilised
by pollen brought from other flowers on the same tree, than from flowers
on a distinct tree. But we should bear in mind that with the
horse-chestnut, for instance, only one or two of the several flowers on
the same peduncle produce a seed; and that this seed is the product of
only one out of several ovules within the same ovarium. Now we know from
the experiments of Herbert and others that if one flower is fertilised
with pollen which is more efficient than that applied to the other
flowers on the same peduncle, the latter often drop off (10/41.
'Variation under Domestication' chapter 17 2nd edition volume 2 page
120.); and it is probable that this would occur with many of the
self-fertilised flowers on a large tree, if other and adjoining flowers
were cross-fertilised. Of the flowers annually produced by a great tree,
it is almost certain that a large number would be self-fertilised; and
if we assume that the tree produced only 500 flowers, and that this
number of seeds were requisite to keep up the stock, so that at least
one seedling should hereafter struggle to maturity, then a large
proportion of the seedlings would necessarily be derived from
self-fertilised seeds.
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