The Hidden Memories of Plants

Do plants form memories? They don't form new synapses in their brain cells, because they do not have brain cells. But if you look at learning and memory as observed changes in behavior, plants certainly do conform their behavior to changes in their environment. We once thought their behavior was genetic, the result of the survival of the fittest, and that plants either lived or died in the conditions in which they sprout. But experiments show that plants can adapt their behavior to conditions not found in their normal environment -and remember those behavioral adaptations over time. Evolutionary ecologist Monica Gagliano first worked with animals, and when she switched to plant studies, took some of the animal experimental techniques with her in a study on how plants learn and retain their lessons. 

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.”

This kind of learning is what plants do to the best of their ability, in order to survive in a world with changing temperatures, amount of sunlight, and water supply. But how? Is it genetic, epigenetic, or some secret chemical process? Read about the research into plant memory at Atlas Obscura.