The high-flying physics of a plant’s exploding fruits
When it’s time for the hairyflower wild petunia to pass its genes to the next generation, it does it with a bang.
To reproduce, the plant flings tiny seeds from a small torpedo-shape fruit more than 20 feet through the air. That’s not an easy task.
The seeds are discs about a tenth of an inch in diameter — smaller than the circles that fall out of a hole punch — and 1/50th an inch thick, the equivalent of three sheets of paper.
“It’s like throwing confetti,” said Dwight Whitaker, a professor of physics at Pomona College in Claremont, Calif.
In an article published in the Journal of the Royal Society Interface, Dr. Whitaker and a trio of undergraduate physics majors worked out what happens in that moment of explosion that launches the seeds so far.
“It’s really cool,” said Sheila Patek, a professor of biology at Duke University who was not involved with the research.
While scientists know that plants use a variety of strategies to disperse seeds, Dr. Whitaker and his students “really did an exceptional job of showing how this comes together in this particular plant species,” Dr. Patek said.
Dr. Whitaker became intrigued with the hairyflower wild petunia more than five years ago when botanists at Rancho Santa Ana Botanic Garden, less than a mile from campus, told him about the plant.
The seeds sit within a small fruit that is a bit over an inch long. A spine along each half of the fruit is made of three layers, which shrink at different rates as they dry. That creates a strain that bends them outward. The two halves remain held together by glue.