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The Four Whorls of a FlowerThe parts and functions of a flower are much more detailed than they might appear at first glance. If you look at a flower from the top, you will be able to distinguish between four "whorls," or circular sections that share a common center. The outer whorl is called the calyx, and consists of the sepals. The next whorl is the corolla, and consists of the petals. The two innermost whorls are the stamens and the carpels, and those contain the male and female reproductive parts of the flower respectively.
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Whorl #1: The Calyx
The calyx, which is the outermost whorl of a flower, protects the inner whorls, especially when the flower is in its bud state. The calyx is made up of sepals, which are two small green structures at the flower's base that look like tiny leaves.
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Whorl #2: The Corolla
The second whorl of the flower is the corolla, which is composed of the flower's petals. The petals serve two purposes: to protect the reproductive organs of the flower and to attract pollinators. Because of this second purpose, they are usually brightly colored and scented so that animals and insects will come close to them and move around the flower's pollen. The first two whorls of the flower -- the calyx and the corolla -- are collectively called the perianth.
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Whorl #3: The Stamens
The third whorl of a flower is the stamen, the male reproductive part. The stamen is made of a thin vertical thread-like structure called a filament topped with a circular or oblong structure called an anther. The anther produces pollen, which is the male contribution to the reproduction process in plants.
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Whorl #4: The Carpels
At the center of the flower is the fourth whorl -- the carpels, which contain the pistil of the flower. The pistil is the plant's female reproductive organ, which is composed of three parts: the ovary, the style, and the stigma. The ovary contains the eggs, or ovules, of the plant, and when the ovules are fertilized, the ovary sometimes turns into a fruit to house the seed. The top of the ovary leads to a vertical structure called a style, which supports the stigma. The stigma catches grains of pollen that the wind or pollinators disperse, and the pollen grains travel down the style to the ovary.
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Other Parts Their Functions
Other, less commonly defined parts of a flower include the pedicel, or the stalk of the flower; the nectary, which secretes nectar; and the floral axis, a term which describes the section of the flower containing the four whorls. Understanding these lesser-known parts of a flower and their functions is an important part of understanding why a flower is an important part of a plant.
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NBII. "How Does That Flower Work?" http://www.nbii.gov/portal/server.pt/community/learn_about_pollination/872/what_is_a_pollinator/2913
Memorial University. "Molecular Biology of Flower Development." http://www.mun.ca/biochem/courses/3107/Topics/Flower_development.html
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WP Clipart. "Mature Flower Diagram." http://www.wpclipart.com/plants/diagrams/Mature_flower_diagram.png.html