Saturday, November 17, 2012

Under Fire in Israel - Adventures with an Exploding Cucumber

In a seemingly uninteresting and weed infested wasteland in Jerusalem I discovered a patch of miniature pendulous cucumbers attached to upright stalks. Almost overlooking it, I did a double take as this conformation is uncommon in nature. I then recalled having seen this in a David Attenborough movie. This movie starlet turned out to be Ecballium elaterium, better known as... the 'Exploding Cucumber'.

I cautiously reached over to touch a fruit. Blam! The fruit was gone in a hail of seeds and flying globs of gelignaceous fluid. Setting up the video camera, I managed to capture this choleric plant in action ( Drawing the attention of a two local Israelites, we proceeded to investigate the properties of the fruit. Standing five metres away I was literally pipped on the head. We extended the range to 10m and our heroic target became the subject of a shotgun attack, with cucurbitaceous bullets scattering all around him. So much for 6-10ft as stated in Wikipedia! Slightly yellow fruits are the best, and the merest touch elicits this dehiscent response. Walking through an extended mat of them is truly one of the most exciting experiences it is possible to have with plants, with popping, snapping, squirting seeds flying everywhere! While investigating them I noted them to be home to a plethora of insects including flower-visiting wasps and bees.

Wikipedia (1) reveals that the fruit is highly toxic due to being laced with bitter cucurbitans (titerpenoids). That would explain the typical twisted-expression-inducing taste and smell that one encounters with so many wild cucurbs. In the ancient world this plant was also deemed to be an abortifacient. In Turkey, fresh juice applied to the nostrils has been found to be beneficial in treating sinusitus.

The mechanism of dispersing seeds mechanically is known as autochory. Some well-known examples are Impatiens (I remember the joy and wonder when touching these seeds as a kid), and the yellow-flowered weed Oxalis corniculata. The mechanism is described in an article in (2). Apparently the tissue around the seed is converted into a mucilagenous tissue that greatly increases the turgor pressure within the fruit. When the pressure is released at the aperture of connection - baddabing baddaboom!

Some questions remain: Does the fruit of the plant still obtain water with such a high turgor pressure, and if so, how? The fruit is green - so how significant is the photosynthesis of the fruit in increasing the turgor pressure? This latter question can be tested to some extent by covering it from light during development and seeing if the fruit still explode.


(2) K. Pushkar. Dispersal of Seeds. Competition Science Vision, Oct. 1985. p. 1083.

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