05-08-2017, 03:31 PM
Sunflower pollination:
Sunflower blossoms are suitable for insect pollination because crowding of flowers ensures notoriety and pollination of a maximum number of flowers by a single insect visit. The honey, secreted in the base of the style, is protected by the tube of the corolla of insects of short tongue. When the flower opens, the receptive surfaces of the two stigmas are pressed together and occupy a position at the base of the tube formed by the joined anthers; The latter is divided into the interior and the released pollen fills the cavity of the tube and exposes it to contact with the visiting insects. Fianll, the style protrudes through the anther tube and the stigmas separate and expose their previously concealed receptive surfaces. Thus, the life story of the flower falls into two stages, the first male and the second female. This favors cross-pollination compared to self-pollination. Therefore, the sun flower is virtually self-sterile, although self-pollination may take place at a late stage when cross-pollination has failed.
Self-pollination:
Self-pollination is when the pollen of the same plant reaches the stigma of a flower (in flowering plants) or in the egg (in Gymnosperms). There are two types of self-pollination: In the autogame, pollen is transferred to the stigma of the same flower. In geitonogamy, pollen is transferred from the anther of a flower to the stigma of another flower on the same flowering plant, or from the microsporangium to the ovule within a single gymnosperm (monoecious). Some plants have mechanisms that guarantee autogamy, such as flowers that do not open (cleistogamia), or stamens that move to come into contact with stigma.
