Squirting cucumbers, or Ecballium elaterium, are little gourds with an intriguing dispersal strategy – they explosively squirt their seeds over distances hundreds of times their length. This incredible ability has stumped naturalists for a very long time, since the days of the Roman Empire. Finally, a group of scientists have unraveled the mystery.
This explosive method to disperse seeds happens extremely quickly, taking only 0.03 seconds. Once ripe, a hairy green fruit, roughly 4 cm long, drops from a stem. As it falls, the fruit blasts out a fountain of seeds and sticky liquid at approximately 20 m per second, with the seeds reaching distances as far as 10 m.
In the study published in the Proceedings of the National Academy of Sciences, the research group used high-speed video, time-lapse photography, CT scans, and digital 3D reconstructions to get to the bottom of this ballistic mystery. While a buildup of liquid and release of internal pressure play a part, the plant’s physical changes before and during the explosion can shape the spew’s angle, height, and distance.
The scientists found that a fluid gradually accumulates within the fruit and stem weeks before the dispersal event, causing the stem to become stiff and the fruit to position to an angle of 45 degrees. This angle enables the cucumber to spit its seeds farther. During the first hundreds of microseconds of ejection, the tip of the stem shrinks away from the fruit, causing the fruit to spin in the opposite direction, which enables it to disperse the seeds more widely.
These findings may apply to various fields. For example, drones, underwater vehicles, or fluid-based propulsion systems could use similar methods to move or change direction swiftly in different environments. It could also give insight into technologies like soft robotics.’