Pollination occurs when pollen grains are transferred from the anther to the stigma of a flower. This is usually done by visiting insects, most often bees, in search of nectar.
For self-pollinating varieties this can be done by transfer of pollen grains from the anther to the stigma of the same flower.
Varieties that require cross pollination need pollen grains from a flower of another variety to be transferred to the stigma of its flower.
Although a flower can be pollinated it may not be fertilized in which weather can be the biggest factor. Some varieties are self-pollinating, in which production can be increased by cross-pollination with another variety.