Aquatic plants are, very often, terrestrial plants living in water. The pollen grains are destroyed, when they come into contact with water. The aquatic plants having pollen which cannot withstand the contact with water, need means for pollen transport or, anyhow a possibility to avoid destruction of the pollen grains. A ”natural” way of escaping the water is flowering above the water surface. Some specializations on this principle are e.g. found in Ottelia (Hydrocharitaceae): the flower opens and closes in accordance with the rippling of the water surface caused by air currence. The flower rests on the water surface and, when submerged, closes and keeps and retains an air bubble. The air movement within the flower causes pollen transport.