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.

Drip some water onto it, the glue dissolves and the fruit violently splits in half.

With ultrahigh speed video — up to 20,000 frames a second — Dr. Whitaker and his students slowed down the action, watching as hooks in the fruit accelerated the seeds to speeds more than 30 miles per hour, similar to how the curved scoops used in the sport of jai alai can accelerate a ball to well over 100 m.p.h.

“It just looks like this gentle, beautiful motion,” Dr. Whitaker said.

Image Seeds still nestled in the jagged stalks that help propel the hairyflower wild petunia's seeds. Credit... Erin Tripp

When they did the calculations, they were stunned to find that some of the seeds were spinning at a rate of more than 1,600 revolutions a second. The discs were oriented vertically, spinning like a bicycle wheel headed backward. Those at the top of the fruit tended to fly the farthest, while those at the bottom of the fruit tended to wobble — “floppers,” the researchers call them — and land closer to where they started.

Next, they wondered why. Why the vertical orientation? Why backspin? Why do the seeds spin so fast?

For that, they turned to an obsolete piece of 20th century technology: the compact disc. Carolyn Cross, who graduated from Pomona in 2013, cannibalized a boom box and built a disc-launching apparatus.

She also performed more prosaic experiments: flinging CDs down a hallway or off the roof of a campus building.

No matter how she launched the CDs, the spinning discs would invariably tip over to a vertical orientation, always with back spin, not top spin.