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
From the foregoing twenty-seven illegitimate plants, fertilised with their own-
form pollen, twenty-five seedling grandchildren were raised; and these were all
long-styled; so that from the two illegitimate generations fifty-two plants were
raised, and all without exception proved long-styled. These grandchildren grew
vigorously, and soon exceeded in height two other lots of illegitimate seedlings
of different parentage and one lot of equal-styled seedlings presently to be
described. Hence I expected that they would have turned out highly ornamental
plants; but when they flowered, they seemed, as my gardener remarked, to have
gone back to the wild state; for the petals were pale-coloured, narrow,
sometimes not touching each other, flat, generally deeply notched in the middle,
but not flexuous on the margin, and with the yellow eye or centre conspicuous.
Altogether these flowers were strikingly different from those of their
progenitors; and this I think, can only be accounted for on the principle of
reversion. Most of the anthers on one plant were contabescent. Seventeen flowers
on the grandchildren were illegitimately fertilised with pollen taken from other
seedlings of the same lot, and produced fourteen capsules, containing on an
average 29.2 seeds; but they ought to have contained about 35 seeds. Fifteen
flowers legitimately fertilised with pollen from an illegitimate short-styled
plant (belonging to the lot next to be described) produced fourteen capsules,
containing an average of 46 seeds; they ought to have contained at least 50
seeds. Hence these grandchildren of illegitimate descent appear to have lost,
though only in a very slight degree, their full fertility.
We will now turn to the short-styled form: from a plant of this kind, fertilised
with its own-form pollen, I raised, during February 1862, eight seedlings, seven
of which were short-styled and one long-styled. They grew slowly, and never
attained to the full stature of ordinary plants; some of them flowered
precociously, and others late in the season. Four flowers on these short-styled
seedlings and four on the one long-styled seedling were illegitimately
fertilised with their own-form pollen and produced only three capsules,
containing on an average 23.6 seeds, with a maximum of 29; but we cannot judge
of their fertility from so few capsules; and I have greater doubts about the
normal standard for this union than about any other; but I believe that rather
above 25 seeds would be a fair estimate. Eight flowers on these same short-
styled plants, and the one long-styled illegitimate plant were reciprocally and
legitimately crossed; they produced five capsules, which contained an average of
28.6 seeds, with a maximum of 36. A reciprocal cross between legitimate plants
of the two forms would have yielded an average of at least 57 seeds, with a
possible maximum of 74 seeds; so that these illegitimate plants were sterile
when legitimately crossed.
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