Reproduction: How Life Continues
Pollination
Find out how pollen travels from one flower to another.
Does a flower need pollen to make fruit? An experiment with peas. Pea flowers were covered with muslin bags in different ways. Every bagged flower formed fruit except the bud whose stamens had been removed. So pollen must reach the stigma for fruit to form. Moving pollen from an anther to a stigma is pollination.
Two kinds:
- Self-pollination: pollen reaches the stigma of the same flower, or another flower on the same plant.
- Cross-pollination: pollen reaches a flower on another plant of the same kind.
Who carries the pollen? Each flower is built for its helper:
| Carrier | Examples | The flowers have |
|---|---|---|
| Wind | Wheat, maize, rice | Light, small pollen in huge amounts; long, feathery stigmas |
| Water | Vallisneria, Hydrilla | Pollen carried by water currents |
| Insects (bees, butterflies) | Sunflower, hibiscus, marigold | Bright colours, nectar, scent; large, sticky or spiky pollen; sticky stigmas |
| Birds (Indian white-eye, sunbirds) | Coral tree, hibiscus | Pollen picked up as birds feed |
Picture a bee visiting a flower for nectar: pollen sticks to its hairy legs and body, and rubs off on the sticky stigma of the next flower.
Which way wastes less pollen? (Table 11.3)
| Pollen grains per flower | Seeds | |
|---|---|---|
| Wind-pollinated grasses | 5,00,000 to 10,00,000 | 50 to 200 |
| Insect-pollinated sunflower | 20,000 to 40,000 | 800 to 1,000 |
Insects deliver pollen far more efficiently. Wind wastes most of it, so wind-pollinated plants make up for it with enormous numbers.
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