At the center of the experiment was the plant Mimosa pudica, which has a dramatic response to unfamiliar mechanical stimuli: Its leaves fold closed, perhaps to scare away eager herbivores. Using a specially designed rail, Gagliano introduced her M. pudica to a new experience. She dropped them, as if they were on a thrill ride in an amusement park for plants. The mimosa plants reacted. Their leaves shut tight. But as Gagliano repeated the stimulus—seven sets of 60 drops each, all in one day—the plants’ response changed. Soon, when they were dropped, they didn’t react at all. It wasn’t that they were worn out: When she shook them, they still shut their leaves tight. It was as if they knew that being dropped was nothing to freak out about.
Three days later, Gagliano came back to the lab and tested the same plants again. Down they went, and … nothing. The plants were just as stoic as before.
This was a surprise. In studies of animals such as bees, a memory that sticks for 24 hours is considered long-term. Gagliano wasn’t expecting the plants to keep hold of the training days later. “Then I went back six days later, and did it again, thinking surely now they forgot,” she says. “Instead, they remembered, exactly as if they had just received the training.”
She waited a month and dropped them again. Their leaves stayed open. According to the rules that scientists routinely apply to animals, the mimosa plants had demonstrated that they could learn.
In the study of the plant kingdom, a slow revolution is underway. Scientists are beginning to understand that plants have abilities, previously unnoticed and unimagined, that we’ve only ever associated with animals. In their own ways, plants can see, smell, feel, hear, and know where they are in the world. One recent study found that clusters of cells in plant embryos act a lot like brain cells and help the embryo to decide when to start growing.
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In their experiments, however, Crisp and Eichten don’t observe many plant memories being formed. What if, they ask, plant memory is rare simply because it’s better for plants to forget? “Having a memory, keeping track molecularly of signals that you’ve received in the past from your environment, does have a cost,” says Eichten. “Since we don’t see memories all that often … maybe plants don’t want to remember things all the time. Maybe it’s better to put their energies elsewhere.” Even when memories do form, they can fade. Another research group has shown, for example, that a plant might form an epigenetic memory of salt stress and pass it along across generations, but that if the stress fades, so does the memory. A plant that remembers too much might sacrifice healthy growth to be constantly on guard against drought, flood, salt, insects. Better, perhaps, to let those negative experiences go, instead of always preparing for the worst.
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“In that context, memory is actually not the interesting bit—of course you have memory, otherwise you wouldn’t be able to do the trick,” she says. “Memory is part of the learning process. But—who is doing the learning? What is actually happening? Who is it that is actually making the association between fan and light?”
It’s telling that Gagliano uses the word “who,” which many people would be unlikely to apply to plants. Even though they’re alive, we tend to think of plants as objects rather than dynamic, breathing, growing beings. We see them as mechanistic things that react to simple stimuli. But to some extent, that’s true of every type of life on Earth. Everything that lives is a bundle of chemicals and electrical signals in dialogue with the environment in which it exists. A memory, such as of the heat of summer on last year’s beach vacation, is a biochemical marker registered from a set of external inputs. A plant’s epigenetic memory, of the cold of winter months, on a fundamental level, is not so different.- The Hidden Memories of Plants
Three days later, Gagliano came back to the lab and tested the same plants again. Down they went, and … nothing. The plants were just as stoic as before.
This was a surprise. In studies of animals such as bees, a memory that sticks for 24 hours is considered long-term. Gagliano wasn’t expecting the plants to keep hold of the training days later. “Then I went back six days later, and did it again, thinking surely now they forgot,” she says. “Instead, they remembered, exactly as if they had just received the training.”
She waited a month and dropped them again. Their leaves stayed open. According to the rules that scientists routinely apply to animals, the mimosa plants had demonstrated that they could learn.
In the study of the plant kingdom, a slow revolution is underway. Scientists are beginning to understand that plants have abilities, previously unnoticed and unimagined, that we’ve only ever associated with animals. In their own ways, plants can see, smell, feel, hear, and know where they are in the world. One recent study found that clusters of cells in plant embryos act a lot like brain cells and help the embryo to decide when to start growing.
[---]
In their experiments, however, Crisp and Eichten don’t observe many plant memories being formed. What if, they ask, plant memory is rare simply because it’s better for plants to forget? “Having a memory, keeping track molecularly of signals that you’ve received in the past from your environment, does have a cost,” says Eichten. “Since we don’t see memories all that often … maybe plants don’t want to remember things all the time. Maybe it’s better to put their energies elsewhere.” Even when memories do form, they can fade. Another research group has shown, for example, that a plant might form an epigenetic memory of salt stress and pass it along across generations, but that if the stress fades, so does the memory. A plant that remembers too much might sacrifice healthy growth to be constantly on guard against drought, flood, salt, insects. Better, perhaps, to let those negative experiences go, instead of always preparing for the worst.
[---]
“In that context, memory is actually not the interesting bit—of course you have memory, otherwise you wouldn’t be able to do the trick,” she says. “Memory is part of the learning process. But—who is doing the learning? What is actually happening? Who is it that is actually making the association between fan and light?”
It’s telling that Gagliano uses the word “who,” which many people would be unlikely to apply to plants. Even though they’re alive, we tend to think of plants as objects rather than dynamic, breathing, growing beings. We see them as mechanistic things that react to simple stimuli. But to some extent, that’s true of every type of life on Earth. Everything that lives is a bundle of chemicals and electrical signals in dialogue with the environment in which it exists. A memory, such as of the heat of summer on last year’s beach vacation, is a biochemical marker registered from a set of external inputs. A plant’s epigenetic memory, of the cold of winter months, on a fundamental level, is not so different.- The Hidden Memories of Plants
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