You don’t need a dandelion to know which way the wind blows. But it can help.
Dandelion seeds fly free in the wind. But those on any given dandelion have different destinies. Some are primed to float north. Others are fated to fly east, south or west — or some direction in between. Each is programmed to release on a wind coming from one direction. It resists winds from all other directions. That finding was shared at the American Physical Society’s Division of Fluid Dynamics meeting last November 20. The meeting was held in Indianapolis, Ind.
How dandelion seeds respond to the wind depends on where they sit on the seed head, says Jena Shields. She’s a biophysicist at Cornell University in Ithaca, N.Y. The feathery seeds on the side facing a breeze will let go most easily. The others hold on tens to hundreds of times more tightly — until the wind shifts.
The research was inspired by a child. Shields’ adviser was watching his toddler play with dandelions. He noticed that the flowers’ seeds didn’t all come off the same. Some came loose more easily than others, but it depended on how they blew on the seed heads. So Shields set out to study what was going on.
She measured the force it takes to pluck dandelion seeds. To start, she superglued a fine wire to the tufted ends. Then she pulled them from the seed heads at various angles. This seed-by-seed study mimicked what happens when the wind, or someone’s breath, pushes them over.
Each seed released most easily for winds from one direction, Shields confirmed. That helps prevent seeds from one head all going the same way. And it may explain why the plants are so successful at spreading. Once blown off a dandelion, a seed’s umbrella-like tuft carries it on the breeze that pulled it away.
One exception: “A strong, turbulent wind can still send all the seeds flying in the same direction,” Shields says. So a powerful gust — or an excited child — can blow off all the seeds at once.