The flower is a reproductive part of an agiospermic plant. The flower serves the purpose of sexual reproduction. In a typical flower, there are four kinds of whorls. These whorls are successively arranged on the swollen end of the stalk or pedicel.
The swollen end of the stalk is called thalamus or receptacle.
Whorls of Flower:
Calyx: The outermost whorl of a flower is called calyx. It is composed of sepals. Sepals are usually green and leaf-like structures. The sepals protect the flower during the bud stage. Calyx is called gamosepalous when sepals are united and is called polysepalous when sepals are free.
Corolla: The second whorl of a flower is called corolla. It is composed of petals. Petals are usually brightly coloured. The bright colours attract the insects and birds for pollination. Corolla is called gamopetalous when petals are united and is called polypetalous when petals are free. Corolla can be tubular, bell-shaped, funnel-shaped or wheel-shaped.
Androecium: The third whorl of a flower is called androecium. It is composed of stamens. A stamen is composed of a stalk and an anther. An anther is usually a bilobed structure. There are two chambers (pollen sacs) in each lobe of an anther. Pollen sacs produce pollen grains. A sterile stamen is called staminode.
Gynoecium: The central whorl of a flower is called gynoecium. It is composed of one or more carpels. A carpel is composed of three parts. The basal swollen portion is called ovary. The long tubular part over ovary is called style and the flat top at the style is called stigma. The style is the receptive surface for pollen grains. Each ovary bears one or more ovules which are attached to a flattened, cushion-like placenta.