D.C., Pollination's Capital

By Adrian Higgins
Washington Post Staff Writer
Thursday, April 12, 2007

Why are the trees powdering us with pollen? It's nothing personal; we're bystanders in a messy spring mating game. Pollen contains male sex cells in search of a female gamete to fertilize.

Many plants -- the Japanese flowering cherry trees, lilies and apple trees -- use insects to transfer pollen from male to female. This is efficient and beneficial to everyone involved: The plant has to make far fewer pollen grains, the insect gets a snack of pollen or nectar, and delivery is more or less assured. But more-primitive plants rely on a cruder dispersal method, air currents. This is so hit-or-miss that the culprits have to produce ridiculously large amounts of feather-light pollen, most of which never hits its target. Scientists have calculated that in the lower third of Sweden, for example, spruce trees unleash 75,000 tons of pollen each year. "Imagine how much would be in a ton when you can put them on a pinhead," said Vaughn Bryant, a pollen scientist at Texas A&M University.

In Washington, which is surely no better off than Stockholm, the offenders include pine, oak, ash, elm, birch and willow. Later in the spring, grasses will kick in. In late summer until the first frost, ragweed will leave other plants, and us, in the dust.

At this time of year, one cubic meter of air can contain as many as 100,000 grains of pollen. The average person inhales 12 cubic meters of air daily, Bryant said, creating the potential for an intake of . . . oh, it doesn't bear thinking about. Pass the Kleenex.

© 2007 The Washington Post Company