Pollination is the process whereby pollen grains move from the anther to the stigma on a flower’s style, while fertilization is the fusion of the male gametes and female egg cells to form a new plant seed. Pollination precedes fertilization and depends on such media as wind, water and insects. Pollination takes place externally, while fertilization occurs in the inside of the flower and does not depend on external vectors.
If no suitable agent of pollination is present to carry pollen from one plant to another, a plant can pollinate itself in a process called self-pollination. In this case, male gametes are transferred from the anther to the stigma of the same flower or to the stigma of another flower of the same plant. However, some plants have strategic mechanisms to prevent self-pollination. The style starts off being taller than the anther, making self pollination physically impossible. If no agent of pollination shows up, the anther grows taller than the style and pollinates it. The fertilized seeds that arise from self-pollination are not as good as those from cross-pollination. They are usually genetically identical to the parent plant. If the parent plant has deformities, so do the offspring. Cross-pollination remains an excellent way of fertilizing hybrid seeds, sometimes in controlled laboratory conditions.