The Different Forms of Flowers on Plants of the Same SpeciesDarwin, Charles
Science
The Different Forms of Flowers on Plants of the Same Species
Darwin, Charles
Fertilization of plants; Heterostylism; Plant physiology; Plants -- Variation; Pollination
That this is a variation, and not a third or distinct form, as in the trimorphic
genera Lythrum and Oxalis, is clear; for we have seen its first appearance in
one out of a lot of illegitimate long-styled plants; and in the case of Mr.
Duck’s seedlings, long-styled plants, only slightly deviating from the normal
state, as well as equal-styled plants were produced from the same self-
fertilised parent. The position of the stamens in their proper place low down in
the tube of the corolla, together with the small size of the pollen-grains,
show, firstly, that the equal-styled variety is a modification of the long-
styled form, and, secondly, that the pistil is the part which has varied most,
as indeed was obvious in many of the plants. This variation is of frequent
occurrence, and is strongly inherited when it has once appeared. It would,
however, have possessed little interest if it had consisted of a mere change of
structure; but this is accompanied by modified fertility. Its occurrence
apparently stands in close relation with the illegitimate birth of the parent
plant; but to this whole subject I shall hereafter recur.
[Primula auricula.
Although I made no experiments on the illegitimate offspring of this species, I
refer to it for two reasons:--First, because I have observed two equal-styled
plants in which the pistil resembled in all respects that of the long-styled
form, whilst the stamens had become elongated as in the short-styled form, so
that the stigma was almost surrounded by the anthers. The pollen-grains,
however, of the elongated stamens resembled in their small size those of the
shorter stamens proper to the long-styled form. Hence these plants have become
equal-styled by the increased length of the stamens, instead of, as with P.
Sinensis, by the diminished length of the pistil. Mr. J. Scott observed five
other plants in the same state, and he shows that one of them, when self-
fertilised, yielded more seed than an ordinary long- or short-styled form would
have done when similarly fertilised, but that it was far inferior in fertility
to either form when legitimately crossed. (5/8. ‘Journal of the Proceedings of
the Linnean Society’ 8 1864 page 91.) Hence it appears that the male and female
organs of this equal-styled variety have been modified in some special manner,
not only in structure but in functional powers. This, moreover, is shown by the
singular fact that both the long-styled and short-styled plants, fertilised with
pollen from the equal-styled variety, yield a lower average of seed than when
these two forms are fertilised with their own pollen.
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