Pollination is the transfer of pollen from anther to stigma, essential because the stamens and pistil sit spatially apart; it is direct in gymnosperms (pollen lands on an exposed ovule) and indirect in angiosperms (pollen lands on an enclosed stigma), and most flowers are chasmogamous (open, exposing anthers/stigma) though some, like Commelina benghalensis's underground flowers, are cleistogamous (self-pollinated without ever opening). By destination, pollination is self-pollination/autogamy (same flower, only possible in bisexual flowers) or cross-pollination/allogamy, which is either geitonogamy (another flower of the same plant - functionally cross- but genetically equivalent to self-pollination) or xenogamy (a genetically different plant of the same species). Flowers promoting self-pollination use cleistogamy or homogamy (stamens and stigma mature together, e.g. Mirabilis jalapa); flowers promoting cross-pollination use contrivances such as dicliny/unisexuality (monoecious, e.g. coconut, still allows geitonogamy; dioecious, e.g. Borassus, blocks both autogamy and geitonogamy), or, within bisexual flowers, dichogamy (protandry - stamens mature first, e.g. Clerodendrum; or protogyny - stigma matures first, e.g. Scrophularia), herkogamy (stamens and stigma physically kept apart, e.g. the reflexed style of Gloriosa), heterostyly (distyly in Primula, tristyly in Lythrum - pollination only between matching organ lengths) and self-incompatibility (pollen cannot germinate on its own stigma, e.g. Abutilon). Pollinating agents are abiotic - anemophily (wind; reduced, scentless, nectarless flowers with abundant light pollen and large feathery stigmas, e.g. maize, whose tassel sheds pollen caught by the cob's long silk) and hydrophily (water; epihydrophily at the surface, e.g. Vallisneria's floating male flowers settling on a surfaced female flower; hypohydrophily fully submerged, e.g. Zostera's neutrally-buoyant pollen) - or biotic (zoophily): ornithophily by birds (large, tubular, brightly coloured, nectar-rich, scentless flowers, e.g. Erythrina), cheiropterophily by bats (nocturnal, strongly scented, e.g. Adansonia digitata, where the bat …