A flower is the reproductive structure of plants that produce seeds. It is usually composed of four main parts: sepals, petals, stamens and carpels. The sepals are the modified leaves that protect the flower before it blooms, while the petals are the modified leaves that usually give the flower its color and attractiveness. The stamens are the male structures that produce pollen, and the carpels are the female structures that contain the ovules. When pollination occurs, pollen is transferred from the stamen to the carpel, where it fertilizes the ovule and produces a seed.