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A flower is the reproductive organ of those plants classified as angiosperms
(flowering plants; Division Magnoliophyta). The function of a flower is to
produce seeds through sexual reproduction. For the higher plants, seeds are
the next generation, and serve as the primary means by which individuals of
the species are dispersed across the landscape.
A flower has four main parts (starting from the base and working inwards):
* calyx is the outer whorl of sepals; usually these are green.
* corolla is the whorl of petals, which are usually thin, soft, and
colored, to attract insects that help the process of pollination.
* androecium (from Greek andros: man) consists of the stamens, each a
filament topped by an anther where pollen is produced. Pollen contains
the male gametes.
* gynoecium (from Greek gynos: woman) consisting of a pistil, with one or
more carpels, which are the female reproductive organs and contain an
ovary with ovules (female gametes).
Some species of plants produce separate male (containing the stamens) and
female (containing the pistil) flowers. In some of these species, an
individual plant is either male or female and the species is regarded as
dioecious; in others, male and female flowers appear on the same plant and
then the species is called monoecious. In the majority of species,
individual flowers have both pistils and stamens. Some of these flowers are
capable of self-fertilization, which increases the chance of producing
seeds, but limits genetic variation. The extreme case of this occurs in
flowers that always self-fertilize, such as the common dandelion.
Conversely, some species of plants have ways of preventing
self-fertilization. Male and female flowers on the same plant may not appear
at the same time, or pollen from the same plant may be incapable of
fertilizing its ovules.
A major function of flowers in nature is simply to attract animals to
pollinate the flower, the movements of the pollinating agent contributing to
the opportunity for genetic recombinations within a dispersed plant
population. Bees and birds are common pollinators: both have color vision,
thus selecting for "colorful" flowers. Some flowers have patterns that are
evident in the ultraviolet range, visible to bees but not to humans. Flowers
also attract pollinators by scent. In any case, pollinators are attracted to
the plant, perhaps in search of nectar, which they eat. The arrangement of
the stamens insures that pollen grains are transfered to the bodies of the
pollinator. In gathering nectar from many flowers of the same species, the
pollinators transfer pollen between all of the flowers.
Flower scent is not always pleasant to our nose. Some plants, such as
Rafflesia and the titan arum, are pollinated by flies, so produce a scent
imitating rotting meat. Other flowers are pollinated by the wind, and these
species (for example, the grasses) have no need to attract pollinators and
therefore tend not to be "showy".
Flowers in the Arts
The great variety of delicate and beautiful flowers has inspired the works
of many poets.
Ah, Sun-flower weary of time,
Who countest the steps of the Sun,
Seeking after that sweet golden clime
Where the traveller's journey is done:
Where the Youth pined away with desire,
And the pale Virgin shrouded in snow
Arise from their graves, and aspire
Where my Sun-flower wishes to go.
– William Blake, Ah! Sun-Flower