How a plant can tell whether you’re wearing a blue or red shirt as you’re approaching it.
As I was planting my seasonal crop of tomatoes last month, a good friend (and my personal gardening guru) informed me that they liked their leaves rubbed, “like petting a pet’s ears,” which I received with equal parts astonishment, amusement, and mild concern for my friend. But, as Tel Aviv University biologist Daniel Chamovitz reveals in What a Plant Knows: A Field Guide to the Senses (public library), that might not be such a crazy idea after all. Plants, it turns out, possess a sensory vocabulary far wider than our perception of them as static, near-inanimate objects might suggest: They can smell their own fruits’ ripeness, distinguish between different touches, tell up from down, and retain information about past events; they “see” when you’re approaching them and even “know” whether you’re wearing a red or blue shirt; like us, they have unique genes that detect light and darkness to wind up their internal clock.
A key reason why plants have evolved such complex sensory system is that, unlike us and our fellow animals, they can’t escape a bad environment, pursue a good one, run away when danger approaches, or get up for a glass of water. Their “rootedness,” which keeps them immobile, is an enormous evolutionary constraint and, like all such constraints, responsible for a great many adaptations. Chamovitz explains:
While most animals can choose their environments, seek shelter in a storm, search for food and a mate, or migrate with the changing seasons, plants must be able to withstand and adapt to constantly changing weather, encroaching neighbors, and invading pests, without being able to move to a better environment. Because of this, plants have developed complex sensory and regulatory systems that allow them to modulate their growth in response to ever-changing conditions. An elm tree has to know if its neighbor is shading it from the sun so that it can find its own way to grow towards the light that’s available. A head of lettuce has to know if there are ravenous aphids about to eat it up so that it can protect itself by making poisonous chemicals to kill the pests. A Douglas fir tree has to know if whipping winds are shaking its branches so it can grow a stronger trunk. Cherry trees have to know when to flower.
Even though plants don’t have a central nervous system where this “knowledge” resides and is enacted, their sophisticated vessels connect their various parts into one responsive whole. In many ways, Chamovitz points out, plants are significantly less genetically different from us than we tend to think — yet his arguments are reserved and rooted in research, far from arguing that plants are just like us. What does emerge from What a Plant Knows, however, is a fascinating inside look at what a plant’s life is like, and a new lens on our own place in nature.
Scientific American has an interview with Chamovitz.