We are led, therefore, to conclude
that the rule of increased sterility in accordance with increased inequality in
length between the pistils and stamens, is a purposeless result, incidental on
those changes through which the species has passed in acquiring certain
characters fitted to ensure the legitimate fertilisation of the three forms.
Another conclusion which may be drawn from Tables 4.23, 4.24, and 4.25, even
from a glance at them, is that the mid-styled form differs from both the others
in its much higher capacity for fertilisation in various ways. Not only did the
twenty-four flowers legitimately fertilised by the stamens of corresponding
lengths, all, or all but one, yield capsules rich in seed; but of the other four
illegitimate unions, that by the longest stamens of the short-styled form was
highly fertile, though less so than the two legitimate unions, and that by the
mid-length stamens of the long-styled form was fertile to a considerable degree;
the remaining two illegitimate unions, namely, with this form's own pollen, were
sterile, but in different degrees. So that the mid-styled form, when fertilised
in the six different possible methods, evinces five grades of fertility. By
comparing Tables 4.24.3 and 4.24.6 we may see that the action of the pollen from
the shortest stamens of the long-styled and mid-styled forms is widely
different; in the one case above half the fertilised flowers yielded capsules
containing a fair number of seeds; in the other case not one capsule was
produced.
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