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
Dried flowers of this plant, which grows in small wet ditches in St. Catharina,
in Brazil, were likewise sent me by Fritz Muller. In the long-styled form the
exserted stigma stands rather above the level of the exserted anthers of the
other form; whilst in the short-styled form it stands on a level with the
anthers of the other form. So that the want of strict correspondence in height
between the stigmas and anthers in the two forms is reversed, compared with what
occurs in Hedyotis. The long-styled pistil is to that of the short-styled as 100
to 36 in length; and its divergent stigmas are longer by fully one-third of
their own length than those of the short-styled form. In the latter the anthers
are a little larger, and the pollen-grains are as 100 to 80 in diameter,
compared with those from the long-styled form.
Cinchona micrantha (Rubiaceae).
Dried specimens of both forms of this plant were sent me from Kew. (3/26. My
attention was called to this plant by a drawing copied from Howard’s
‘Quinologia’ Table 3 given by Mr. Markham in his ‘Travels in Peru’ page 539.) In
the long-styled form the apex of the stigma stands just beneath the bases of the
hairy lobes of the corolla; whilst the summits of the anthers are seated about
halfway down the tube. The pistil is in length as 100 to 38 to that of the
short-styled form. In the latter the anthers occupy the same position as the
stigma of the other form, and they are considerably longer than those of the
long-styled form. As the summit of the stigma in the short-styled form stands
beneath the bases of the anthers, which are seated halfway down the corolla, the
style has been extremely shortened in this form, its length to that of the long-
styled being, in the specimens examined, only as 5.3 to 100! The stigma, also,
in the short-styled form is very much shorter than that in the long-styled, in
the ratio of 57 to 100. The pollen grains from the short-styled flowers, after
having been soaked in water, were rather larger--in about the ratio of 100 to
91--than those from the long-styled flowers, and they were more triangular, with
the angles more prominent. As all the grains from the short-styled flowers were
thus characterised, and as they had been left in water for three days, I am
convinced that this difference in shape in the two sets of grains cannot be
accounted for by unequal distension with water.
Public-domain text, read in full here on John Shaqi.
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