<P> Self - pollination is when pollen from the same plant arrives at the stigma of a flower (in flowering plants) or at the ovule (in gymnosperms). There are two types of self - pollination: in autogamy, pollen is transferred to the stigma of the same flower; in geitonogamy, pollen is transferred from the anther of one flower to the stigma of another flower on the same flowering plant, or from microsporangium to ovule within a single (monoecious) gymnosperm . Some plants have mechanisms that ensure autogamy, such as flowers that do not open (cleistogamy), or stamens that move to come into contact with the stigma . The term selfing that is often used as a synonym, is not limited to self - pollination, but also applies to other types of self - fertilization . </P> <P> Few plants self - pollinate without the aid of pollen vectors (such as wind or insects). The mechanism is seen most often in some legumes such as peanuts . In another legume, soybeans, the flowers open and remain receptive to insect cross pollination during the day . If this is not accomplished, the flowers self - pollinate as they are closing . Among other plants that can self - pollinate are many kinds of orchids, peas, sunflowers and tridax . Most of the self - pollinating plants have small, relatively inconspicuous flowers that shed pollen directly onto the stigma, sometimes even before the bud opens . Self - pollinated plants expend less energy in the production of pollinator attractants and can grow in areas where the kinds of insects or other animals that might visit them are absent or very scarce--as in the Arctic or at high elevations . </P> <P> Self - pollination limits the variety of progeny and may depress plant vigor . However, self - pollination can be advantageous, allowing plants to spread beyond the range of suitable pollinators or produce offspring in areas where pollinator populations have been greatly reduced or are naturally variable . </P>

Give example of self pollination and cross pollination
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