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
The pistil occupies the position represented in Figure 4.10, with its extremity
considerably upturned, but to a variable degree; the stigma is seated between
the anthers of the longest and the shortest stamens. The six longest stamens
correspond in length with the pistil of the long-styled form; their filaments
are coloured bright pink; the anthers are dark-coloured, but from containing
bright-green pollen and from their early dehiscence they appear emerald-green.
Hence in general appearance these stamens are remarkably dissimilar from the
mid-length stamens of the long-styled form. The six shortest stamens are
enclosed within the calyx, and resemble in all respects the shortest stamens of
the long-styled form; both these sets correspond in length with the short pistil
of the short-styled form. The green pollen-grains of the longest stamens are 9
to 10 in diameter, whilst the yellow grains from the shortest stamens are only
6; or as 100 to 63. But the pollen-grains from different plants appeared to me,
in this case and others, to be in some degree variable in size. The capsules
contain on an average 130 seeds; but perhaps, as we shall see, this is rather
too high an average. The seeds themselves, as before remarked, are smaller than
those of the long-styled form.
SHORT-STYLED FORM.
The pistil is here very short, not one-third of the length of that of the long-
styled form. It is enclosed within the calyx, which, differently from that in
the other two forms, does not enclose any anthers. The end of the pistil is
generally bent upwards at right angles. The six longest stamens, with their pink
filaments and green pollen, resemble the corresponding stamens of the mid-styled
form. But according to H. Muller, their pollen-grains are a little larger,
namely 9 1/2 to 10 1/2, instead of 9 to 10 in diameter. The six mid-length
stamens, with their uncoloured filaments and yellow pollen, resemble in the size
of their pollen-grains and in all other respects the corresponding stamens of
the long-styled form. The difference in diameter between the grains from the two
sets of anthers in the short-styled form is as 100 to 73. The capsules contain
fewer seeds on an average than those of either of the preceding forms, namely
83.5; and the seeds are considerably smaller. In this latter respect, but not in
number, there is a gradation parallel to that in the length of the pistil, the
long-styled having the largest seeds, the mid-styled the next in size, and the
short-styled the smallest.
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