Three summers ago, Kiel University biomechanist Stainslav Gorb, returned to Germany after a vacation in Turkey with a present for Ph.D. student Helen Gorges.
"He came back and was like, 'Helen, I brought you something. They might explode, but maybe you can work on them,'" she recalls.
He presented her with a handful of squirting cucumbers, a smaller, hairier cousin of what one would find in the produce aisle — except that it's toxic.
But what the squirting cucumber lacks in palatability, it makes up for in a feat of ballistic seed dispersal. When the fruit is ripe, it's puffed up with fluid, pressurized, and ready to burst.
The merest disturbance or nudge causes the cucumber to pop open and expel its seeds in a fraction of a second, sending seeds on a germination journey that can reach some distance away, reducing competition with their parent.
Once Gorges learned about this botanical feat, she was hooked. "We just wanted to know how the whole explosion works," says Gorges.
She and her colleagues have done just that in a talk she gave at last week's Society for Experimental Biology conference in Belgium and an upcoming publication in the journal npj Science of Plants. "The plant is crazy," summarizes Gorges. "The fruit really prepares for perfect dispersal — as far as possible so that the plant will grow everywhere."
A cucumber's perfect ballistic angle
Gorges and her colleagues started figuring out how the cucumber worked by taking a few hundred photos of the plants — some from Turkey and others from the local botanical garden in Kiel in northern Germany — to measure the angle between the stem and the ripened fruit.
It was consistently a touch more than 50 degrees. "With air resistance," she says, "it just is the perfect angle so that they can shoot as far as they can — the perfect ballistic angle for the perfect shooting parabola."
Next, Gorges examined the fifty-some seeds inside the fruit. But cut one open, and the whole thing explodes. So she took micro-CT scans of the fruit's interior, which revealed the seeds lined up in rows, awaiting their launch, round end first. "The seeds, they really all come out in the same direction," says Gorges.
To examine the expulsion of the seeds in greater detail, she used high speed videography.
When Gorges later slowed down the video, she observed the stem lifting off and a jet of fluid spurting out, accompanied by one seed shooting out at a time. She calculated that the seeds can reach velocities of up to nearly 30 miles an hour and they can launch themselves almost 40 feet.
The results are consistent with a study published in 2024 in the journal PNAS by a different team in England that calculated an average launch angle of about 43 degrees, velocities of 37 miles per hour, and launch distances of almost 40 feet.
"It's actually very difficult to throw a small object a large distance," says Dwight Whitaker, a physicist at Pomona College who didn't contribute to either research project. "To my knowledge, [this is] one of the few plants, if not the only plant, that uses a fluid to eject its seeds — this pressurized fluid that sort of pushes them and accelerates them as they come out."
A supremely sticky seed
Gorges then examined the seeds' slimy coat.
When she placed a seed on a glass slide and let it dry, she found its adhesive quality was so strong that a single seed could support as much as a six-pound weight.
"If adhesion is what it's all about," says Sheila Patek, a biologist at Duke University who wasn't involved in the research, "then in fact, the remarkable launch velocities may have more to do with making sure that when that seed hits something, it sticks" — so that it might then be carried farther by whatever it's stuck to.
To test this idea, future work could consider how well the seeds adhere to various surfaces when launched at different speeds.
Patek says that the discoveries about the squirting cucumber may well have many applications. "These types of materials are really translatable in today's world of material science," she says, including soft robotics that might disperse seeds on farms or deliver drugs in the human body.
And these seeds, whose stickiness changes when wet, could help inspire materials designed to work differently in damp or dry conditions.
Not bad for a little squirt.
Copyright 2025 NPR
