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How Venus flytraps work

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Without muscles to help them, some plants and fungi move rapidly to shake off predators, spread their seeds or slap pollen on visiting insects, and new research helps describe these quick moves.

To understand how a Venus flytrap closes its leaves, imagine cutting a tennis ball in half. If you forced one half of the ball inside out, you could feel how the ball "wants" to flip back to its original position.

When a Venus flytrap is waiting for an insect, its leaves are curved like the inside-out half of a tennis ball. The swelling of cells with extra water triggers the leaf to flip back to its original curved position.

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This rapid plant movement is called "snap buckling." It gives the Venus flytrap a quick way to close and trap an insect between its leaves.

Jan Skotheim and L. Mahadevan from Harvard University in Cambridge, Massachusetts used math to explain how the movement of water inside plants determines how fast cells can swell. These swelling cells trigger the rapid closing of the fly-catching leaves.

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The scientists thought they had the snapping shut of leaves all figured out, until they stumbled across a smaller insect-catching plant that looks like a Venus flytrap but is one-tenth the size and closes its leaves in a different way. The mysterious leaves of the insect-eating Aldrovanda plant don't flip between right-side-out and inside out in order to close them and trap insects.

After a lot of head scratching, number crunching and research, the scientist think they can explain the two different leaf-closing techniques. Aldrovanda is so small that its cells can swell with water fast enough to close the leaves smoothly and rapidly without relying on any snapping movements that reverse the way the leaves are curved.

While Jan Skotheim, who is also at the University of Cambridge in Cambridge, UK, was busy thinking about how the heck the two insect-eating plants close their leaves in different ways, his mom, who is an artist, began to illustrate the big ideas behind her son's experiments. One of the collages made it to the cover of this week's issue of Science, 27 May, 2005.

Using the "Hura tree" from Brazil as an example, Jan Skotheim described another kind of exploding plant movement. As the tree's seedpods bake in the sun, the outside cells lose water and shrink more then the cells on the inside lining of the seedpod. This creates a strain that grows and grows until the seed pod tears and the seeds go flying.

Exploding pods, snapping leaves and other rapid plant movements happen so fast your eyes might miss them, but these actions must obey nature's speed limits set by the laws of physics. Science author L. Mahadevan explained that plant tissues can only tear as fast as waves of sound can travel through the plant.

These plants can do some amazing things, but they can't break the sound barrier.