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
This form can be at once recognised by the length of the pistil, which is
(including the ovarium) fully one-third longer than that of the mid-styled, and
more than thrice as long as that of the short-styled form. It is so
disproportionately long, that it projects in the bud through the folded petals.
It stands out considerably beyond the mid-length stamens; its terminal portion
depends a little, but the stigma itself is slightly upturned. The globular
stigma is considerably larger than that of the other two forms, with the
papillae on its surface generally longer. The six mid-length stamens project
about two-thirds the length of the pistil, and correspond in length with the
pistil of the mid-styled form. Such correspondence in this and the two following
forms is generally very close; the difference, where there is any, being usually
in a slight excess of length in the stamens. The six shortest stamens lie
concealed within the calyx; their ends are turned up, and they are graduated in
length, so as to form a double row. The anthers of these stamens are smaller
than those of the mid-length ones. The pollen is of the same yellow colour in
both sets. H. Muller measured the pollen-grain in all three forms, and his
measurements are evidently more trustworthy than those which I formerly made, so
I will give them. (4/2. ‘Die Befruchtung der Blumen’ 1873 page 193.) The numbers
refer to divisions of the micrometer equalling 1/300 millimetres. The grains,
distended with water, from the mid-length stamens are 7 to 7 1/2, and those from
the shortest stamens 6 to 6 1/2 in diameter, or as 100 to 86. The capsules of
this form contain on an average 93 seeds: how this average was obtained will
presently be explained. As these seeds, when cleaned, seemed larger than those
from the mid-styled or short-styled forms, 100 of them were placed in a good
balance, and by the double method of weighing were found to equal 121 seeds of
the mid-styled or 142 of the short-styled; so that five long-styled seeds very
nearly equal six mid-styled or seven short-styled seeds.
MID-STYLED FORM.
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