Just inside the petals is a whorl of stamens. Each stamen is composed of a thin stalk, called a filament, and a saclike anther, where meiosis occurs to form microspores that develop into pollen grains. Each pollen grain produces two cells surrounded by a though outer wall. One cell divides to form two male gametes, or sperm cells, and the other produces a pollen tube through which the sperm cells travel to reach the ovule. In the center of most flowers is one or more carpels, the female reproductive organs.
Carpels bear ovules, which are structures with the potential to develop into seeds.
The carples of a flower may be separate or fused into a single structure. The female part of the flower is also referred to as a pistil. A pistil may consist of a single carpel or a group of fused carpels. The egg and polar nuclei participate directly in fertilization, and, following fertilization, the ovule develops into a seed and the ovary into a fruit. Flowering plants have an alternation of generations in which the sporophyte generation is larger and nutritionally independent and the gametophyte generation is microscopic in size and nutritionally dependent on the sporophyte.