There Is Such a Thing as Plant Intelligence

Plants are capable of solving problems and learning from past experiences.

When Paleolithic painters decorated the walls of the caves at Chauvet, in France, they chose stunning motifs of horses and other animals. For them, as for most of us, plants were just there in the background, vegetating away. Sure, a daisy can be cute, a redwood impressive. But compared to a cheetah or an elephant, most plants are, well, boring.

With his new book, Cabaret of Plants: Forty Thousand Years Of Plant Life and the Human Imagination, British author Richard Mabey pushes back against this prejudice to make us see that plants are as thrilling as animals and have been key to our relationship with the world.        

Speaking from his home in Norfolk, England, he recalls growing up near Harry Potter’s Whomping Willow; why trees were so often the inspiration for myths and magic; and how a woman in Italy has demonstrated that some plants can remember—and learn from—their experiences.

Nature’s superstars are animals like chimps or cheetahs. You think plants are just as amazing. Convince us.
What can plants do that cheetahs can’t? They can regenerate when 90 percent of their bodies have been eaten away. They can have sex at long distances and communicate with approximately 20 more senses than an animal has. Those are very pragmatic arguments. But I think they’re valuable just because they’re there. We tend to judge plants not as autonomous organisms but in terms of what they can do for us. But they’re astonishing in their own right and deserve to be given the same ethical status as animals.

The seventies classic The Secret Lives of Plants claimed carrots screamed when picked. The “new botany” is making similar claims about plant intelligence. Are those claims just as whacky?
No! [Laughs] I think that seventies generation believed plants were not only intelligent but conscious, which is a dramatically different thing. What the new botany is suggesting is that plants are sensitive and problem solving but bypass the need for self-consciousness and brain activity that we assume is necessary for intelligence. People who think this are often accused of being anthropocentric, believing that plants are behaving like humans. The philosopher Daniel Dennett marvelously riposted that critics of this theory are "cerebrocentric," believing intelligent behavior is not possible without the infinitely superior human brain. What the new work shows is that plants, by means we do not yet fully understand, are capable of behaving like intelligent beings. They are capable of storing—and learning from—memories of what happens to them.

Tell us about Monica Gagliano’s experiments with mimosa pudica, aka the "sensitive plant."
Monica Gagliano is a very gifted and off-the-wall plant physiologist, or "plant neurobiologist," as she likes to call herself. She did this famous experiment where she potted up a number of mimosa plants, long known as the "sensitive plant." As far back as the 18th century, it was known to react to any kind of touch or threat by curling up its leaves, in sequence, up the stems.
What Gagliano did was simulate the touch action by dropping these potted mimosas a fixed distance to the ground, so they received a mild physical shock. To start with, all of them closed their leaves in the proscribed fashion. On the second and third drop, rather less did. And by the end of a large number of drops, none of them were closing up. 

Conventional botanists who saw the experiment said, “They’re just tired!” [Laughs] But she repeated the experiment with the same plants a week, and then a month, later. They all responded in the same way: They didn’t react to being dropped by folding up their leaves. But when they were simulated in the conventional way, like being grasped by a hand, they all immediately closed up.

In this engraving after British artist George Romney, Emma Hamilton, mistress of Admiral Horatio Nelson, poses as 'Sensibility' next to a mimosa pudica, known as the 'sensitive plant.' [Photograph by Universal History Archive, Getty]

By comparison, bees can only retain memories of places to find honey for three days. But the mimosa plants appeared to be able to "remember" the difference between an apparent and a real threat, and retained this discrimination in their memory.

We all know about the World Wide Web. But you describe something called the “wood wide web.” Tell us about it.
It’s long been known that the trees in a forest are connected by mycorrhizal fungi. This means fungi that live symbiotically with the roots of forest trees. The forest trees can’t grow without them because they haven’t got enough access to the minerals in the soil, and the fungi can’t grow without the trees because they have no chlorophyll and therefore can’t manufacture sugars. It's a beautiful symbiosis in which all trees are involved.

What has now begun to be discovered is that the mycorrhizal fungi don’t surround just one tree. By using radioactive trace elements, the researchers were able to show that nutrients were being passed by the fungi between different species of trees over a large area. The trees that were not so good in the winter, like aspens, were being given food manufactured by the conifers, which do much better in winter, and vice versa. So the fungus is actually helping to distribute food amongst forest trees so that they all benefit at the right time.
Messages about predators are also being sent. If a tree is attacked by insects, pheromonic chemicals are distributed through the mycorrhizal fibers beneath the soil, as well as being blown through the air by the trees, to warn other trees that an insect attack is imminent and to prepare themselves by producing more tannin in their leaves. [Laughs] It’s quite a chatty system.

As a boy, Mabey explored the ancient woodlands at Ashridge Estate, above, home of a giant beech tree that was the model for the Whomping Willow in the Harry Potter movies. [Photograph by Helen Dixon, Alamy]

Plants employ amazingly ingenious methods to propagate. Tell us about some of your favorites.
I think the orchids are the only plant family on Earth to use sex pheromones to attract insects rather than the enticing smell of nectar. The insects are drawn inside because they experience a chemical message from the orchid similar to the one they get from a female of the same species. Having entered the orchid, attracted by this scent, they are then manipulated by the orchids in intriguing ways: They are taken through mazes, in which they pick up pollen, or flip trap doors that shut them inside the orchid. When the bees fly out, they are super-charged sexually and so attract more females.

How is climate change altering the plant landscape? Are you pessimistic?
I probably should be pessimistic but I’m temperamentally an optimist. Obviously when climate change is dramatic, like in parts of North Africa, where you’re getting the advance of desert at an amazing rate and spectacular droughts, it’s going to have a profound impact on plant life. In more temperate areas, like Britain, if we assume that the current run of very mild, wet winters is part of climate change, what it’s doing is promoting the spread of plants capable of surviving wet conditions, and also promoting much later flowering. Plants that normally flowered in the spring or summer are now either continuing to flower into winter, or having a second flowering, something very common in the Mediterranean region.

One of the discoveries being made is that Lamarck’s theory, which was discredited for a century, is now being shown to be true. Acquired characteristics can be inherited. The new science of epigenetics is finding that a number of changes produced in organisms during their own lifetime are passed on to their offspring. So far, it’s a limited number. But stresses due to climate, virus invasion or changes in soil can actually change the genome of the organism.

The automatic assumption that plants are victims, incapable of learning how to cope with new conditions, is an insult and runs contrary to the new evidence.

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