Scientists have discovered the explosive secret behind one of nature's most dramatic seed dispersal methods: the squirting cucumbers.
The plant, Ecballium elaterium, lives up to its name by firing its seeds at high speed over enormous distances, and a new study from Kiel University, Germany has captured the process in greater detail than ever before.
The ripening fruits of the squirting cucumber fill with thick fluid, building up to an intense internal pressure. When fully ripe, the stem detaches and the fruit violently ejects its seeds.
“Mostly this happens when the fruit is very ripe and something touches the fruit e.g. animals, insects or rain,” the study’s lead Helen Gorges, from Kiel University, Germany, told BBC Science Focus.
“The plant just wants to disperse the seeds as far as possible and in this way it can shoot them over 12 metres (39 ft) away from the base plant.”
As even the slightest brush could set the fruits off, Gorges’ team used CT imaging to create a 3D model of the fruit without destroying them.
Then they used high-speed cameras, shooting at 1,000 and 10,000 frames per second to capture the moment the cucumbers ballistically fired their seeds at up to 47 km/h (29mph).
Gorges also watched the plants as their fruit ripened. She found the fruit stem straightened over time, until the cucumbers were hanging at an angle of 52º just before they detonated. The theoretically perfect ballistic shooting angle is 50º, so the cucumbers are almost dead on target.
Like many plants, the cucumbers spread their seeds as far as they can to reduce the competition for light, water and nutrients between the parent plant and its offspring.
While most plants evolved to use the wind, waterways or animals to carry away their seeds, the squirting cucumber took matters into its own hands with its ballistic method.
The research team hope that what they’ve learned could lead others to create nature-inspired solutions to future challenges.
“There are also many applications in soft robotics, drug delivery systems and similar devices, where energy-efficient launching systems are desired,” said Gorges.
About the expert
Helen Gorges is a PhD student from the Department of Functional Morphology and Biomechanics at Kiel University, Germany, studying how plants are optimised to distribute their seeds.
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