NEXT TIME WE SMELL THAT SCENT AFTER FRESH CUT GRASS OR PICKING FLOWERS, NOW WE KNOW IT IS A PLANT SCREAMING.
When a leafy plant is under attack, it doesn't sit quietly. Back in 1983, two scientists, Jack Schultz and Ian Baldwin, reported that young maple saplings getting bitten by insects release a spurt of chemicals that float through the air. You and I wouldn't notice, but these chemicals carry a slight odor that neighboring plants can detect. It's a little like a silent scream.
The chemicals the plants pump through the air are a blend of organic molecules — alcohols, aldehydes, ketones and esters — known as volatile organic compounds, VOCs for short.
They pump out attractants — perfumes designed to lure in different airborne insects — in this case, wasps. Wasps are an aphid's worst nightmare. Once they arrive, the tables are turned. The critter who was lunching now becomes lunch.
in study after study it appears that these chemical conversations help the neighbors. The damage is usually extensive on the first plant, but the neighbors, relatively speaking, stay pest-resistant. Apparently, they heard the alarm and knew what to do.
Not only do plants use airborne chemicals, they send signals underground, through their roots. Some make ultrasonic "clicking" sounds. What feels to us like a quiet day in the forest may in fact be a hurly-burly of wafting, pulsing, clicking plant-to-plant communication.
And sometimes the chatter leaps across species lines. Scientists have simulated an animal attack on a sagebrush. In the American West, pronghorn antelopes regularly grab on to sage with their teeth and tear off leaves when it's time for lunch ...
In the lab version, as the animal's teeth ripped the sage leaves, scientists watched the sage plant send a chemical signal into the air, and watched as a nearby tobacco plant picked up the signal and then emitted an odor that was noxious to the animal — strong enough to repel the antelope — protecting itself, and, arguably, helping the sage. What a complex dance!
Charles Darwin, 150 years ago, imagined a world far busier, noisier and more intimate than the world we can see and hear. Our senses are weak. The world is buzzing. Darwin sensed this. "Let it be borne in mind how infinitely close-fitting are the mutual relations of all organic beings to each other," he wrote. I like that expression, "infinitely close-fitting." It suggests there's a whole lot going on, and that we're just hearing our first peep.