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TWO KINDS OF POLLEN

Some plants create pollen that is light and dusty; some create pollen that is heavy and sticky. These are useful because they allow pollination to happen in different ways.

If the pollen is light and dusty, it can blow on the wind. Some of the pollen lands on the stigma of a compatible flower, just by chance. Grasses often use this approach to pollination. The anthers have to make a lot of pollen, since most of it will never reach a female flower. If you ever visit a corn field while the plants are pollinating, you can actually see the pollen in the air, on the leaves, and on the ground. This is very expensive for the plants, but they do not have to produce colourful flowers or nectar to attract insects.

If the pollen is heavy and sticky, it can't blow on the wind. Plants that make this kind of pollen need insects to carry it from flower to flower. They have to create big colourful flowers to attract insects, and they have to create sweet nectar to lure the insects inside. Their pollen is often also a more nutritious food source. All of this costs the plant a lot of energy, but it saves on the amount of pollen that it has to produce. Only a tiny amount of pollen is needed, since the insects act as an efficient delivery service.

Quiz

1. Do ragweed plants need insect pollinators?

2. Does goldenrod cause hayfever allergies?

3. Which can pollinate further, corn or pumpkins?

Answers

1. Ragweed has very light, dusty pollen that blows on the wind. You can tell because the flowers are small and not showy, so they aren't meant to attract insects, and especially because the pollen causes allergies. People who suffer from hayfever are breathing ragweed pollen. In late summer, the small plants create so much wind-borne pollen that everyone winds up breathing it. Only a tiny amount ever lands on another ragweed flower to do its real job.

2. Goldenrod is often blamed for allergies, but it has heavy, sticky pollen that never travels on the wind. Hayfever sufferers are really allergic to ragweed pollen, but the bright, showy goldenrod flowers are more obviously visible. It's just a coincidence that they bloom at the same time of year.

3. Corn has light, dusty wind-blown pollen. Pumpkins have large, yellow, nectar-rich, insect-attracting flowers, and heavy pollen that can only be spread by insects. The question is: which travels further, the wind or the insects? The answer is that insects will only travel a maximum of about 100 meters during their daily feeding, but the wind can blow pollen up to three kilometers away.





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