The Flower
The flower is the reproductive unit in the angiosperms. It is meant for sexual reproduction. A typical flower has four different kinds of whorls arranged successively on the swollen end of the stalk or pedicel, called thalamus or receptacle. Calyx, corolla, androecium and gynoecium are reproductive organs. In some flowers like lily, the calyx and corolla are not distinct and are termed as perianth.
Parts of Flower
Each flower normally has four floral whorls, viz, calyx, corolla, androecium and gynoecium.
Calyx: The calyx is the outer most whorl of the flower and the members are called sepals. Generally, sepals are green, leaf like and protect the flower in the bud stage. The calyx may be gamosepalous(If sepals united) or polysepalous(If sepals free).
Corolla: Corolla is composed of petals. Petals are usually brightly colored to attract insects for pollination. Like calyx, corolla may be also free(gamopetalous) or united(polypetalous). The shape and color of corolla vary greatly in plants. Corolla may be tubular, bell shaped, funnel shaped or wheel shaped.
Androecium: Androecium is composed of stamens. Each stamen which represents the male reproductive organ consists of a stalk or a filament and an anther. Each anther is usually bilobed and each lobe has two chambers, the pollen-sacs. The pollen grains are produced in pollen sacs. A sterile stamen is called staminode.
Stamens of flower may be united with other members such as petals or among themselves. When stamens are attached to the petals, they are epipetalous as in brinjal or epiphyllous when attached to the perianth as in the flowers of Lilly. The stamens in a flower may be united into one branch or one bundle(monoadelphaous) as in china rose or two bundles(diadekphous) as in pea or into more than two bundles(polyadelphous) as in citrus. There may be a variation in the length of filaments within a flower, as in Salvia and Mustard.
Gynoecium: Gynoecium is the female reproductive part of the flower and is made of up of one or more carpels. A carpel consists of three parts namely stigma, style and ovary. Ovary is the enlarged basal part on which lies the elongated tube, the style. The style connect the ovary to the stigma. The stigma is usually at the tip of the style and is the receptive surface for pollen grains. Each ovary bears one or more ovules attached to a flattened cushion like placenta. When more than one carpel is present, they may be free(as in the lotus and rose) and are called apocarpous. They are termed syncarpous when carpels are fused as in mustard and tomato. After fertilization the ovules develop into seeds and the ovary matures into a fruit.