Pollination is the transfer of pollen grains from the stamen to the stigma of a flower. There are two main types of pollination: cross-pollination which is the transfer of pollen between two different plants, and self-pollination which is the transfer of pollen within the same flower or plant. Pollination can be carried out by insects, wind or water, with the main agents being insects like bees and butterflies, or the wind. Insect-pollinated flowers tend to be large, brightly colored with scents to attract insects, while wind-pollinated flowers are smaller and dull colored without scents.