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Flowers allow certain plants called angiosperms to reproduce, so it's not surprising that botanists refer to different parts of a flower in terms of male and female reproductive organs.
Female Reproductive System: The carpel or pistil is in the very center of the flower and contains the female organs. There may be one or more pistils. This part of a flower resembles a bowling pin in shape with the rounded lower base being the ovary. Inside the ovary are reproductive cells or ovule. Coming up from the ovary the pistil narrows into a neck called the style, and the knob at the top of the neck is the stigma. This part of a flower is sticky. When pollen grains adhere to the stigma via fertilization or pollination from bees, wind or any other means, pollen tubes grow inside the style or neck, and travel down to burrow in the ovary or base. Here the sperm fertilizes an ovum or reproductive egg cell (the singular of ovule). Eventually the ovum develops into a seed.
Some plants don't have to rely on chance for fertilization as they also contain the different parts of a flower that make up the male reproductive organs. These organs produce pollen.
Male Reproductive System: The stamen is that part of a flower that looks like a thin hair with a follicle on top. Usually there are several stamens surrounding the pistil(s). The hair is called the filament and the follicle is the anther where pollen is produced. The filament and anther together make up the stamen.
Flowers that have both the male and female reproductive organs are called perfect flowers while those that only have one or the other are imperfect flowers.
In addition to the pistil (female organs) and stamen (male organs) the outermost whorl is made of petals, while the small, delicate leaves at the base of the petals are the sepals. The sepals are collectively called the calyx. Below the calyx is the stem or peduncle.
Flowers that have pistil, stamens, petals and sepals are called complete flowers. Flowers that lack one or more of these parts are called incomplete flowers.
Flowers that rely on pollinators like hummingbirds and bees commonly produce nectar to attract them and bright colors to call attention. Birds and bees possess color vision and some flowers even have nectar guides -- patterns that show up clearly in the ultraviolet range, visible to bees but not humans. When hummingbirds reach deep into the flower to get nectar, or when bees explore the blossom, pollen grains adhere to the animals to be transferred to other flowers, and pollen from other flowers gets deposited. Hence, pollination occurs.
Aside from the standard blossom described above, there are other types of flowers, like composite flowers. The sunflower and daisy are two common examples. Composite flowers are so named because they are actually a composition of dozens of tiny flowers — two types — that are organized to look like a single flower! The center of a sunflower or a daisy is made up of scores of miniature flowers packed next to each other called disk flowers, while each petal of the sunflower or daisy is a ray flower. Together the ray and disk flowers form many common blossoms. Alternately, dandelions have heads that are made only of ray flowers, while thistles have heads composed only of disk flowers.