Plants don’t have ears. But they can still detect sound
Another, published last year, found that marigolds and sage plants exposed to the noise of traffic from a busy motorway suffered stunted growth, and produced a range of stress compounds. Other research, much of it done in China, reports that certain frequencies, played in acoustically controlled environments like greenhouses, can affect seed germination and even boost crop yields. And plants can make noises, too, albeit not deliberately.
Earlier this year a group of researchers at Tel Aviv University published an article in Cell Press, reporting that several species of plants emitted different noises in response to different stresses—although not at the sorts of frequencies that humans can hear. If all that sounds strange, perhaps it should not. After all, sound carries useful information about an organism’s environment.
From an evolutionary point of view, there is no reason to expect that information to be exploited only by animals. Plants have been evolving alongside the insects that pollinate them and eat them for hundreds of millions of years. With that in mind, Heidi Appel, a botanist now at the University of Toledo, and Reginald Cocroft, an entomologist at the University of Missouri, wondered if plants might be sensitive to the sounds made by the animals with which they most often interact.
The researchers recorded the vibrations made by certain species of caterpillar as they chewed on leaves. These vibrations are not powerful enough to produce sound waves in the air. But they are able to travel across leaves and branches, and even to neighbouring plants if their foliage touches.
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