Pollination
Types of Pollination
1. Self-Pollination (Autogamy)
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Pollen is transferred within the same flower or between flowers of the same plant.
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Ensures reproductive success but reduces genetic diversity.
Types of Self-Pollination:
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Autogamy: Pollen from the anther reaches the stigma of the same flower (e.g., Pea, Tomato).
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Cleistogamy: Flowers remain closed, ensuring self-pollination (e.g., Viola, Peanuts).
2. Cross-Pollination (Allogamy)
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Pollen is transferred from one flower to another flower of a different plant of the same species.
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Promotes genetic diversity, making plants more adaptable.
Diagram: Types of Pollination (Self and Cross-Pollination)
(Illustration showing pollen transfer within the same flower vs. between different flowers.)
Pollinating Agents
Since plants cannot move, they rely on external agents for cross-pollination.
| Pollinating Agent | Characteristics of Pollinated Flowers | Examples |
|---|---|---|
| Wind (Anemophily) | Small, light, and dry pollen; long stamens; feathery stigma. | Maize, Wheat, Rice |
| Water (Hydrophily) | Pollen floats on water surface; flowers emerge above water or remain submerged. | Vallisneria, Hydrilla |
| Insects (Entomophily) | Brightly colored petals, nectar, fragrance, and sticky pollen. | Sunflower, Rose, Orchid |
| Birds (Ornithophily) | Large, brightly colored, tubular flowers with nectar. | Hibiscus, Coral Tree |
Diagram: Different Pollination Mechanisms
(Illustration of wind, water, insect, and bird pollination.)
Outbreeding Devices (Mechanisms to Prevent Self-Pollination)
Plants have developed mechanisms to avoid self-pollination and encourage cross-pollination for genetic diversity.
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Dichogamy – The anther and stigma mature at different times.
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Protandry: Anthers mature before stigma (e.g., Sunflower).
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Protogyny: Stigma matures before anthers (e.g., Mustard).
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Self-Incompatibility – Pollen from the same plant is unable to fertilize the ovule due to genetic mechanisms (e.g., Tobacco, Brassica).
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Herkogamy – Structural differences prevent self-pollination (e.g., Hibiscus).
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Heterostyly – Flowers have different lengths of stamens and pistils, making self-pollination difficult (e.g., Primrose).
Conclusion
Pollination is an essential process for fertilization and seed formation in plants. Different pollination mechanisms ensure genetic diversity, leading to healthier and more adaptable plant populations.