Stamens are floral structures containing the male reproductive organs that form sperm-carrying pollen grains. This pollen producing structure consists of an anther and a filament. The anther has a terminal saclike architecture that contains spore-producing cells called microsporocytes, which undergo meiosis and eventually form grains of pollen. Anthers are elevated from the petals and flower body by long slender stalks called filaments. This places the pollen in a position where it is more likely to be picked up by insects, air currents, or rain. At the base of the stamen, small secretory structures called nectaries serve to attract the birds or insects to the anther in flowering species that requiring cross-pollination. In self-pollinating flowers, the stamens are arranged in whorls, sometimes spirals, around the ovary.