How pollination works

The mechanics

Pollination is the transfer of pollen from the male anther to the female stigma of a flower. Fertilisation follows, and seed and fruit come from that. Most flowering plants do better with pollen from a different individual than their own, and some — apples among them — cannot use their own pollen at all. So the pollen has to travel, and plants have two options: wind, or an animal.

Wind pollination is cheap and wasteful. Grasses, most trees of the temperate forest, and the plants behind most hay fever produce vast quantities of light dry pollen and release it to chance. Those plants have no need for petals, scent or nectar, and generally have none — a hazel catkin is not trying to attract anything.

Animal pollination is precise and expensive. The plant produces nectar, scent, colour and pattern, and in return the pollen is carried directly to another flower of the same species. Everything a flower looks like is advertising and payment for that service.

Why flower shape is a filter

A plant does not want every visitor. It wants visitors that will go to another flower of the same species, and flower architecture is how it selects them.

• Corolla depth filters by tongue length. Red clover's 9-10 mm tube is beyond a honey bee's roughly 6 mm reach, so its nectar goes to long-tongued bumblebees. White clover's shallow florets are open to everyone — which is why one of them produces a famous honey and the other does not.
• Poricidal anthers filter by capability. Tomatoes and blueberries release pollen only through a small pore, and only to a bee that can vibrate it out. Honey bees cannot buzz-pollinate at all.
• Colour and pattern filter by vision. Bees see ultraviolet and not red, and many flowers carry ultraviolet nectar guides invisible to us that point directly at the reward.
• Timing filters by season and by hour. Ivy flowers in October for the insects still flying; some flowers secrete only in the morning.

What makes a good pollinator

Effectiveness is not the same as abundance, and the two get confused constantly. A good pollinator carries pollen where it will come off again, visits the same species repeatedly, and does so when the plant is flowering.