Pollination

Pollination is the transfer of pollen grains from the anther to the stigma.

• Self-pollination: from the anther to the stigma of the same flower or of another flower on the same plant.
• Cross-pollination: from the anther of a flower on one plant to the stigma of a flower on another plant of the same species.

• Factors that favour cross-pollination: flowers are unisexual; the stamens and carpels of a flower mature at different times (protandry — stamens mature first; protogyny — carpels mature first); the anthers are lower than the stigma (so pollen cannot fall by itself).
• Pollen is carried by wind, insects, water, birds and man.

• Adaptations for insect pollination: large coloured petals, scent, nectar, sticky pollen, sticky stigma.
• For wind pollination: small dull flowers without scent or nectar, large feathery stigmas, large amounts of light dry pollen.

Cross-pollination gives genetic variation, and better, stronger seeds; self-pollination is more certain but gives less variation.