The capsules were counted on
one uncovered head, and were 289 in number; whilst those on a fine head
from under the net were only 199.]
Each of these lists contains by a mere accident the same number of
genera, namely, forty-nine. The genera in the first list include
sixty-five species, and those in the second sixty species; the Orchideae
in both being excluded. If the genera in this latter order, as well as
in the Asclepiadae and Apocynaceae, had been included, the number of
species which are sterile if insects are excluded would have been
greatly increased; but the lists are confined to species which were
actually experimented on. The results can be considered as only
approximately accurate, for fertility is so variable a character, that
each species ought to have been tried many times. The above number of
species, namely, 125, is as nothing to the host of living plants; but
the mere fact of more than half of them being sterile within the
specified degree, when insects are excluded, is a striking one; for
whenever pollen has to be carried from the anthers to the stigma in
order to ensure full fertility, there is at least a good chance of
cross-fertilisation. I do not, however, believe that if all known plants
were tried in the same manner, half would be found to be sterile within
the specified limits; for many flowers were selected for experiment
which presented some remarkable structure; and such flowers often
require insect-aid.
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