Curiosity

Curiosity

The plant world has some true speed demons

Posted in 12 July 2018

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in the wetlands of South Carolina, a fly alights on a pink surface. As it explores the scenery, the fly unknowingly brushes a small hair. It's sticking up from the surface like a slender sword. As the fly continues to stroll along, it grazes a second hair. All at once, the pink surface closes in from both sides. Two leaves have snapped shut like a huge pair of botanical jaws.

This blur of movement lasted only a tenth of a second. But this fly will never leave this death trap.

"We don't think plants move," says Joan Edwards. She's a botanist at Williams College in Williamstown, Mass. Yet some plants, she notes, "can move so fast you can't catch them with the naked eye."

We tend to picture plants as largely unmoving - rooted in one place until they die. To describe something boring, we say it's "like watching grass grow." But such phrases offer a naïve view of the plant world.

All plants grow, a rather slow form of motion. Many also have the capacity to move rapidly. The snapping jaws of the Venus flytrap (Dionaea muscipula) are perhaps the most famous example. But they are far from the only one. Plants exhibit plenty of impressive actions. Consider the explosive sandbox tree (Hura crepitans). Also known as the dynamite tree, it can fling seeds the length of an Olympic-sized swimming pool. Sundews (genus Drosera) have sticky tendrils that curl around prey. And within seconds of being touched, the aptly named touch-me-not (Mimosa pudica) folds its compound leaves.

Plants have evolved a broad range of approaches to movement. It spans an equally huge spectrum in terms of speed. Roots crawl through the soil at only about 1 millimeter (0.04 inch) per hour. In contrast, some plants have found a way to shoot their seeds into the environment at speeds of tens of meters (more than 100 feet) per second.

The most dynamic plant movements have long captivated scientists.

Take Charles Darwin. Of all plants, he described the Venus flytrap as "one of the most wonderful in the world."

In his 1875 book Insectivorous Plants, he described tests he conducted on this curiosity. He baited some with raw meat. He prodded others with objects as fine as human hairs. He even tested how the plants' traps reacted to drops of chloroform. Darwin never fully unlocked the plant's secrets. Still, he understood that the shape of its leaves played some role in how speedily they could trap prey.

Explainer: What is a computer model?

Modern researchers can study rapid plant movements with a precision that Darwin would envy. A little more than a decade ago, scientists began using high-speed digital cameras and computer modeling to home in on plant motion. Frame-by-frame analyses, along with high-resolution lenses, at long last offered a detailed look at what gives plants their speed.

Emerging evidence now points to a surprising variety of mechanisms. Researchers have turned up contraptions that kick like a soccer player or throw like a lacrosse player. One plant even generates heat to explosively launch its seeds.

Nearly 150 years after Darwin's work, what drives such research remains the same - a fascination with fast-action plants.