The Sentience of Plants

By James Videle

Could plants be sentient?

Are plants simply mindless automatons, going through the motions of sprouting, growing, flowering, fruiting, re-seeding and dying?  Is this a basic process, requiring no thought of temperature, soil moisture, humidity, nutrients, pollinisation and reproduction?  Does it all just occur, coincidentally or, if the processes are somehow deliberate, is it simply nature being nature?  Hmmm…

It seems there is a lot of anthropogenic thinking going on here.  Maybe it is a little too much for the human brain to wrap around the idea that, in fact, plants think, feel, move, associate with their surroundings, express joy and pain and specifically are aware, conscious of, and responsive to sense impressions.

Photo by Matthew Smith (Unsplash)

In 1900 the Bengali biophysicist and botanist Jagdish Chandra Bose taught that plants are not merely passive organisms lacking sense impressions.  Instead, they explore their environments and can learn and change their behavior with specific purpose.  Plants have an electrical nervous system, he claimed, that allows them to transmit information among their roots, stems, leaves, and other parts.

Determined to reveal the wonders of plant perception to the world, Bose described his experiments and their results in his 1902 paper, “Responses in the Living and the Non-Living.”  He wrote how plants grew more quickly when exposed to pleasant music and gentle whispers, and poorly when exposed to harsh music and loud speech.  He even mentioned how plants became depressed when exposed to polluted air and darkening skies.  In short, his work showed that plants could feel pleasure and they could feel pain.

How about movement?

For anyone who has ever grown a vegetable plant, say a tomato or vining bean, one is amazed by the growth that occurs in a very short period.  Once the temperatures are right in the summer, the plant seems to “take off,” knowing no limits in its growth.  Some scientists claim however that the movement of plants is slow, almost stagnant.  But maybe we are defining movement incorrectly.  According to the research article, “Could Plants Be Sentient?” by Calvo et al. (2017), “99% or more of eucaryotic life on this planet is plant, not animal as indicated by the ratio of oxygen to carbon dioxide.  Thus, the commonest form of behaviour is not movement we see but that expressed by plants.”

Photo by Benjamin Balázs (Unsplash)

Further, Calvo describes the differences of the first evolutionary cells of plants and animals.  Animal cells have always required locomotion to acquire nutrients through food, whether animal or plant-based.  Plants acquired the ability to photosynthesize, creating nutrients from light and even capturing them from the air, as well as reaching out with their roots and obtaining them from the soil.

Referring back to Mr. Bose, four years after his retirement, in 1926, he published “The Nervous Mechanism of Plants,” in which he revealed the existence of the nervous system of plants, the phloem—part of the vascular system that rivals the nervous system in animals.  This finding disputed previous claims by scientists stating that plants had no such nervous systems.  In fact, the vascular systems of plants have a dual purpose.  One, they carry organic materials (sugars, proteins, rna, peptides, hormones), and two, they conduct electrical impulses and action potentials.

What about communication?

It appears that plants do have an underground communication system.  In essence, the roots of plants “talk” with the mycellium network underground.  The mycellium (mushrooms) carry nutrients that the plants require in exchange for plant-derived photosynthate, foraging a symbiotic relationship. In the journal article, “Inter-Plant Communication through Mycorrhizal Networks Mediate Complex Adaptive Behaviour in Plant Communities” (2015), Gorzelak et al. assess that,

The Mychorrizal Network (MN) is considered ecologically and evolutionarily significant because of its positive effects on the fitness of the member plants and fungi.  Our understanding of this significance derives from evidence that MNs influence the survival, growth, physiology, health, competitive ability and behaviour of the plants and fungi linked in the network.  How the MN affects the member plants and fungi is increasingly understood to involve plant–fungal–plant communication, and may involve biochemical signalling, resource transfers or action-potential-driven electrical signals.  The responses of the plants and fungi to this communication are rapid, and thus can be described as behavioural responses, allowing us to refocus our understanding of the significance of MNs through the lens of plant behaviour.

It seems also that plants “listen” to insects chewing on them, by form of vibration, and can differentiate between said actions from wind or mere touch.  In “Plants Respond to Leaf Vibrations Caused by Insect Herbivore Chewing” (2014), Appel & Cocroft suggest that,

the vibrations produced by chewing herbivores are an important source of acoustic energy for plants.  If plants can detect and use this conspicuous, reliable and rapidly transmitted source of information about herbivore feeding, tissues far from the site of attack could use feeding vibrations to respond quickly to the threat of herbivory.  A vibration signaling pathway would complement the known signaling pathways that rely on phloem-borne signals, airborne volatiles, or electrical signals.

This reiterates from the sources cited earlier that the phloem acts as the plant’s nervous system.

Photo by Andrea Reiman (Unsplash)

The ancient religious or mythological perspective, Animism—from the latin anima (breath, spirit, life)—is regarded as the most ancient of belief systems.  This belief asserts that all beings:  animals, plants, rocks, rivers, weather systems, and human handiwork (made from organic materials) are animated and alive.  There is historic precedence for sentience of all beings and it appears that we are coming back to this understanding today.

To put it all in a final perspective, PhD Kenneth Worthy writing in Psychology Today, “Are Plants Entering the Realm of the Sentient?” (2014), states,

It’s long overdue for us to stop thinking of humans as the only conscious animals.  If powerful capabilities long thought unique to humans exist not only in other animals but in plants as well, we must truly begin to see greater continuity between ourselves and the rest of nature.

Imagine the realm of possibilities that open up if the idea that communication between plants and us can occur.  Plants are some of the oldest living residents of this earth, developing about 700 million years ago and fungi perhaps 1.3 billion years ago.  Plants and fungi have been around an extremely long time, have survived mass extinctions and extraordinary climate change.  They would have a lot to teach us and we have much to learn.