obdurata, so closely did its flowers
resemble those of the heterostyled species. But on examining the flowers, the
anthers of the long-styled form were found to be entirely destitute of pollen
and less than half the size of those in the other form, the pistil being
perfectly developed. On the other hand, in the short-styled form the stigmas are
reduced to half their proper length, having also an abnormal appearance; whilst
the stamens are perfect. This plant therefore is dioecious; and we may, I think,
conclude that a short-styled progenitor, bearing long stamens exserted beyond
the corolla, has been converted into the male; and a long-styled progenitor with
fully developed stigmas into the female.
From the number of bad pollen-grains in the small anthers of the short stamens
of the long-styled form of Pulmonaria angustifolia, we may suspect that this
form is tending to become female; but it does not appear that the other or
short-styled form is becoming more masculine. Certain appearances countenance
the belief that the reproductive system of Phlox subulata is likewise undergoing
a change of some kind.
I have now given the few cases known to me in which heterostyled plants appear
with some considerable degree of probability to have been rendered dioecious.
Nor ought we to expect to find many such cases, for the number of heterostyled
species is by no means large, at least in Europe, where they could hardly have
escaped notice.
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