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
seed certainly were homostyled; nevertheless their stamens consisted of two
sets, differing in length and in the colour and thickness of their filaments,
but not in the size or colour of their pollen-grains; so that they thus far
resembled the stamens of Lagerstroemia. I found that Cuphea purpurea was highly
fertile with its own pollen when artificially aided, but sterile when insects
were excluded. (4/11. Mr. Spence informs me that in several species of the genus
Mollia (Tiliaceae) which he collected in South America, the stamens of the five
outer cohorts have purplish filaments and green pollen, whilst the stamens of
the five inner cohorts have yellow pollen. He therefore suspected that these
species might prove to be heterostyled and trimorphic: but he did not notice the
length of the pistils. In the allied Luhea the outer purplish stamens are
destitute of anthers. I procured some specimens of Mollia lepidota and speciosa
from Kew, but could not make out that their pistils differed in length in
different plants; and in all those which I examined the stigma stood close
beneath the uppermost anthers. The numerous stamens are graduated in length, and
the pollen-grains from the longest and shortest ones did not present any marked
difference in diameter. Therefore these species do not appear to be
heterostyled.)]
Oxalis (Geraniaceae).
(Figure 4.11. Oxalis speciosa (with the petals removed).
Left: Long-styled.
Centre: Mid-styled.
Right: Short-styled.
S, S, S, stigmas. The dotted lines with arrows show which pollen must be carried
to the stigmas for legitimate fertilisation.)
Public-domain text, read in full here on John Shaqi.
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