شنبه 10 تیر 1391 07:08 ب.ظ
Flowering plants are the dominant type of plants on the earth today (there are about 250000 species). Flowers are therefore the most common plant organs for sexual reproduction.
Flowers produce gametes (sex cells).
Flowers play a key role in pollination. Pollination is the transfer of pollen (containing the male gametes), from the anther of a flower, to the stigma (receptive surface of the female part of the flower) of the same or a different flower.
Parts of the Flower:
|Form and Function|
|Receptacle||Part of flower stalk bearing the floral organs, at base of flower.|
|Sepal||Leaf-like structures at flower base, protects young flower bud.|
|Calyx||All the sepals together form the calyx.|
|Petal||Located in and above the sepals, often large and colourful, sometimes scented, sometimes producing nectar. Often serve to attract pollinators to the plant.|
|Corolla||All the petals together form the corolla.|
|Stamen||Male part of the flower, consisting of the anther and filament, makes pollen grains.|
|Filament||The stalk of the stamen which bears the anther.|
|Anther||The pollen bearing portion of a stamen.|
|Pollen||Grains containing the male gametes. Immature male gametophyte with a protective outer covering.|
|Carpel\Pistil||Female part of the flower. Consisting of the stigma, style and ovary.|
|Stigma||Often sticky top of carpel, serves as a receptive surface for pollen grains.|
|Style||The stalk of a carpel, between the stigma and the ovary, through which the pollen tube grows.|
|Ovary||Enlarged base of the carpel containing the ovule or ovules. The ovary matures to become a fruit.|
|Ovule||Located in the ovaries. Carries female gametes. Ovules become seeds on fertilization.|
The sex of a flower can be described in three ways:
Staminate flowers: Flowers bearing only male sex parts. These are sometime referred to as "male flowers".
Carpellate\Pistillate Flowers: Flowers bearing only female sex parts. These are sometimes referred to as "female flowers".
Hermaphhrodite\Complete flowers: Flowers bearing both male and female sex parts.
In many cases flowers are borne as a group on a common stalk, called an inflorescence. They are many different types of floral inflorescences. The type of inflorescence present is sometimes used to aid in classifying flowering plants. Below are a number of common floral inflorescences.
Flowers are sometimes associated with prominent, often brightly coloured leaves called bracts. In some instances (like in bougainvilleas, heliconias and ginger lillies), the bracts are even more colourful and outstanding than the flowers they surround.
In the heliconia cultivar on the left, the large yellow and red structures are bracts, while the small yellow structures within them are the actual flowers.
The yellow shrimp plant, has large, showy yellow bracts, and smaller white flowers.
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