The transfer of pollen from an anther (the male reproductive organ) to a stigma (the receptive part of the female reproductive organ), either of the same flower (self-pollination) or of a different flower of the same species (cross-pollination). Cross-pollination involves the action of a pollinating agent to effect transfer of the pollen (see anemophily; entomophily; hydrophily). Transfer of pollen is followed by germination of the pollen grain and growth of a pollen tube through the style to deliver the male gametes to the ovule. See also fertilization; incompatibility.