SCIENCE LAB SCARES* : BOTANICAL BOMBARDIERS

At last, scientists work out what makes squirting cucumbers go ballistic. :

The ground-hugging vines of the squirting cucumber Ecballium elaterium might seem like an ordinary weedy plant. But take a closer look at the plant, which grows in dry, barren areas in the Mediterranean, and you'' find '' an extraordinary thing,'' said Chris Thorogood, head of science at the University of Oxford Botanic Garden and Arboretum in England.

The roughly 1.5-inch [ 3.8 centimeter ] fruits of the squirting cucumber contain toxic chemicals and are distinguished in another way from the green rounds you might put on a salad.

'' When they're ripe, they eject their seeds very violently in a stream of mucilage,'' Dr. Thorogood said. They can shoot up to almost 40 feet [ 12 meters ].

It's long been a mystery why and how the plants can carry out this act of vegetative bombardment. In a new paper, Dr. Thorogood and his colleagues share how the squirting cucumber goes ballistic.

Researchers knew that pressure builds up inside the fruits before they blow.

'' Initially, we all thought it was rather straightforward,'' said Finn Box, a physicist at the University of Manchester in England and another author of the study. But they decided to take a closer look, recording high-speed video of the cucumber cannons in action.

It shows that the ripe fruit detaches from the stalk, opening a hole in the cucumber base. From there, seeds emerge at speeds of up to 66 feet per second.

As the fruit detaches, the stem recoils. The fruit rotates backward, changing the angles at which seeds shoot. As slimy fluid spews out, depressurizing the fruit, the seeds' speed drops.

The group also made time-lapse photos of stalks bearing fruit for several days. In the run-up to a seed-squirting event, the ovoid fruits moved from dangling nearly straight down to a roughly 45-degree angle with the stem.

'' That was just something that blew our minds,'' Dr. Box said of the finding.

[ Carolyn Wilke ]