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
A few flowers sent me from Kew had been somewhat injured, so that I cannot say
anything positively with respect to the position and relative length of the
organs in the two forms. But their stigmas differed almost exactly in the same
manner as in the last species; the papillae on the long-styled stigma being
longer than those on the short-styled, in the ratio of 100 to 42. My son
measured nine pollen-grains from the long-styled, and the same number from the
short-styled form; and the mean diameter of the former was to that of the latter
as 100 to 81. Considering this difference, as well as that between the stigmas
of the two forms, there can be no doubt that this species is heterostyled. So
probably is Gilia nudicaulis, which likewise belongs to the Leptosiphon section
of the genus, for I hear from Professor Asa Gray that in some individuals the
style is very long, with the stigma more or less exserted, whilst in others it
is deeply included within the tube; the anthers being always seated in the
throat of the corolla.
Phlox subulata (Polemoniaceae).
Professor Asa Gray informs me that the greater number of the species in this
genus have a long pistil, with the stigma more or less exserted; whilst several
other species, especially the annuals, have a short pistil seated low down
within the tube of the corolla. In all the species the anthers are arranged one
below the other, the uppermost just protruding from the throat of the corolla.
In Phlox subulata alone he has “seen both long and short styles; and here the
short-styled plant has (irrespective of this character) been described as a
distinct species (P. nivalis, P. Hentzii), and is apt to have a pair of ovules
in each cell, while the long-styled P. subulata rarely shows more than one.”
(3/18. ‘Proceedings of the American Academy of Arts and Sciences’ June 14, 1870
page 248.) Some dried flowers of both forms were sent me by him, and I received
others from Kew, but I have failed to make out whether the species is
heterostyled. In two flowers of nearly equal size, the pistil of the long-styled
form was twice as long as that of the short-styled; but in other cases the
difference was not nearly so great. The stigma of the long-styled pistil stands
nearly in the throat of the corolla; whilst in the short-styled it is placed low
down--sometimes very low down in the tube, for it varies greatly in position.
The stigma is more papillose, and of greater length (in one instance in the
ratio of 100 to 67), in the short-styled flowers than in the long-styled. My son
measured twenty pollen-grains from a short-styled flower, and nine from a long-
styled, and the former were in diameter to the latter as 100 to 93; and this
difference accords with the belief that the plant is heterostyled. But the
grains from the short-styled varied much in diameter. He afterwards measured ten
grains from a distinct long-styled flower, and ten from another plant of the
Public-domain text, read in full here on John Shaqi.
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