The German language has the phrase empfindlich wie eine Mimose sein – to be as sensitive as a Mimosa. This plant is known by many common names including sensitive plant, humble plant, shameplant, and touch-me-not. Find out more about the Mimosa plant on Wikipedia.
James Bridle recounts an experiment, also mentioned in the above-linked Wikipedia article, by researcher Monica Gagliano.
…she devised a simple mechanism: a cup attached to a vertical rail which, when released, would drop a mimosa in its pot exactly fifteen centimetres onto a foam pad. The soft thonk of this landing was enough to surprise the plant into closing up its leaves, but not enough to damage it: a scientifically precise stimulus, with a measurable, ecologically relevant response. Mimosa leaves have small hydraulic structures at their base which, by pumping or draining water, allow them to expand and contract, forcing the leaves to curl. The curling is understood to be a response to a threat: either from animal predation, or excessive heat and evaporation.
She kept dropping the plants, over and over again, up to sixty times a session, over multiple sessions. Three hundred and sixty drops a day: a marathon of bumps and shocks. Thonk thonk thonk. It transpired that it only took a few drops – as few as four or five – for the plants to realize that there was no threat, and that it was safe to keep their leaves open (a side test, involving a different stimulus which still elicited the closing response, revealed that they weren’t simply exhausted by the activity). By the end of the sixty-drop sessions, the plants were entirely unbothered by the drop: they had learned to ignore it.
Here is where it becomes interesting:
Gagliano and her colleagues rested and then retested individual mimosas, demonstrating that they retained over time the memory of the drop, and their associated change in behaviour. Mimosas – and, we must now understand, all plants – are not machines. They are more than the sum of a set of pre-programmed actions and reactions. They learn, remember and change their behaviour in response to the world.
Excerpt from Ways of Being by James Bridle