Mimosa pudica: Can plants hear and think?

Our common sense tends to consider plants very distinct living beings from animals. Maybe because they cannot move or respond in the same way as animals do. One may ponder, do plants have feelings? Do plants think? Can they hear? Believe it or not, studies over the years have some answers to these questions.

A thorough review of the literature suggests that plants respond to chemicals. Damaged plants release chemicals which make other plants aware of possible danger (let’s say of a herbivore attack). Monica Gagliano, a researcher currently based at the University of Western Australia has some interesting theories on the subject. Cognition is a process of acquiring and perceiving inputs/information/knowledge and not just about neurons. Since plants also engage in this process, she uses the word ‘cognition’ for plants as well.

A major piece of her research is pertaining to what is called bioacoustics. It looks at sound/vibration in a physical sense. In a particular experiment performed at the University of Bristol, the roots of baby corn plant were used to record its responses to sounds via shining laser. These lasers detect even intrinsic signals. It was found that for a particular frequency of sound roots grow towards the source of the sound. However, this happens only at that particular frequency. But is the plants deciding not to turn on other frequencies or is it that it can’t hear at other frequencies just like a human can’t hear ultrasounds?

In another study, Mimosa plants were chosen for they have the capacity to close their leaves when a stimulus is given. In an experiment, the plants were subjected to a sound that isn’t found in nature. Initially, they responded by pretending dead. But within seconds Mimosa plant showed no response at all. Suggesting that plants have identified the sound as ‘no danger’ and taken a decision to not respond. It also includes experiments to confirm that plants were not exhausted/fatigued affecting their responses. This is called a dishabituation test. This is crucial to suggest that plants are consciously choosing to not respond.

An animal ecologist by training she uses similar approaches to design and conduct experiments on plants as on the animals. She feels that this approach which looks at plants as subjects and not objects have been fruitful. While plants clearly do not have obviously visible organs like a man to perform vital functions their existence, however, cannot be dismissed. A similar point was made in a recent article published in Scientific American. In addition to Monica’s work, the article mentioned Michael Schöner, a biologist at the University of Greifswald in Germany who believes that plant could very well have organs in the form of structures like hair which act as mechanoreceptor for sounds. Schöner adds, “Noise could block information channels between plants, for example, when they need to warn each other of insects.”

One can also mention that it was none other than Charles Darwin to propose that roots in plants are analogous to brains in animals “It is hardly an exaggeration to say that the tip of the radicle thus endowed [with sensitivity] and having the power of directing the movements of the adjoining parts, acts like the brain of one of the lower animals; the brain being seated within the anterior end of the body, receiving impressions from the sense-organs, and directing the several movements.”

In an audio interview given to Jill Cloutier, Monica concludes that more interdisciplinary research is required to support her science and the kind of science she does might bring us to a point where we begin to consider plants as moral beings and might even consider their legal and ethical status in our societies. These may perhaps upset some people as she recollects how in Switzerland a newly amended law which protects the dignity of vegetation raised many cries.

The father of Biodiversity Edward Wilson once said: “Nature holds the key to our aesthetic, intellectual, cognitive and even spiritual..satisfaction”. So whatever comes our way we should happily embrace it for that our understanding of nature and plants will only get better with time.

Reference: