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
Professor Asa Gray states that the plants of this species growing in the Botanic
Gardens at Cambridge, U.S., are short-styled, but that Siebold and Zuccarini
describe the long-styled form, and give figures of two forms; so that there can
be little doubt, as he remarks, about the plant being dimorphic. (3/16. ‘The
American Naturalist’ July 1873 page 422.) I therefore applied to Dr. Hooker, who
sent me a dried flower from Japan, another from China, and another from the
Botanic Gardens at Kew. The first proved to be long-styled, and the other two
short-styled. In the long-styled form, the pistil is in length to that of the
short-styled as 100 to 38, the lobes of the stigma being a little longer (as 10
to 9), but narrower and less divergent. This last character, however, may be
only a temporary one. There seems to be no difference in the papillose condition
of the two stigmas. In the short-styled form, the stamens are in length to those
of the long-styled as 100 to 66, but the anthers are shorter in the ratio of 87
to 100; and this is unusual, for when there is any difference in size between
the anthers of the two forms, those from the longer stamens of the short-styled
are generally the longest. The pollen-grains from the short-styled flowers are
certainly larger, but only in a slight degree, than those from the long-styled,
namely, as 100 to 94 in diameter. The short-styled form, which grows in the
Gardens at Kew, has never there produced fruit.
Forsythia viridissima appears likewise to be heterostyled; for Professor Asa
Gray says that although the long-styled form alone grows in the gardens at
Cambridge, U.S., the published figures of this species belong to the short-
styled form.
Cordia [sp.?] (Cordiaceae).
Fritz Muller sent me dried specimens of this shrub, which he believes to be
heterostyled; and I have not much doubt that this is the case, though the usual
characteristic differences are not well pronounced in the two forms. Linum
grandiflorum shows us that a plant may be heterostyled in function in the
highest degree, and yet the two forms may have stamens of equal length, and
pollen-grains of equal size. In the present species of Cordia, the stamens of
both forms are of nearly equal length, those of the short-styled being rather
the longest; and the anthers of both are seated in the mouth of the corolla. Nor
could I detect any difference in the size of the pollen-grains, when dry or
after being soaked in water. The stigmas of the long-styled form stand clear
above the anthers, and the whole pistil is longer than that of the short-styled,
in about the ratio of 3 to 2.
The stigmas of the short-styled form are seated beneath the anthers, and they
are considerably shorter than those of the long-styled form. This latter
difference is the most important one of any between the two forms.
Gilia (Ipomopsis) pulchella vel aggregata (Polemoniaceae).
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