Plant Intelligence

You won't look at them the same way you used to: plants are living beings with intelligence

The world bestseller by Italian botanist Stefano Mancuso has finally been published in French. The Intelligence of Plants is a stirring book. The author multiplies the evidence supporting his sometimes controversial hypothesis: plants are living beings endowed with a certain form of intelligence. If we only discover this truth today, it is because our culture has prevented us from admitting it. Mancuso therefore calls us to an intellectual, cultural, psychological revolution, to look at plants in a different way. Plants do not have eyes, nose, ears or brains and yet they are able to see, smell, hear. They are sensitive and intelligent beings who know how to organize strategies and solve the most complex problems. It is not for nothing that plants represent 99.5 % of the biomass of our planet. By closing the last page of this book, you will no longer look at the plant that decorates your living room or the garden in which you like to stroll with the same eye. This is one of the great strengths of this book.
Stefano Mancuso is a biologist at the University of Florence. He is the founder of a new discipline: plant neurobiology, and his research has made him famous all over the world. His book The Intelligence of Plants has become a best-seller translated into 21 languages and today in French. Not all his peers agree with him and reject the idea that plants can be endowed with some form of intelligence. This is normal because since Aristotle and a long line of scientists, the plant kingdom has been at the bottom of the ladder of life. First man, then animals, and far behind plants. We see in them the silent and motionless ornaments of our planet. Yet plants represent the bulk of our planet's biomass. Humans and all animals account for less than 0.5 %. If human life were to disappear from this planet, in just a few years, all human constructions, human civilizations, the slightest trace of our passage on Earth, would be replaced by profusions of plant species. Stefano Mancuso gently inflicts on us a narcissistic wound equivalent to those caused by Copernicus, Darwin and then Freud. It is our arrogance and the long time spent with plants that prevent us from recognizing the intelligence of plants.
The author of this disturbing book is accumulating evidence. Although he can sometimes be blamed for his tendency to anthropomorphism, he most often resorts to it for the clarity of his explanations.
For the average person, plants vegetate. They are immobile, they photosynthesize, they produce a new bud from time to time, they make flowers or fruits, they lose their leaves in winter. Nothing more. The expression "vegetative state" often used in a negative way corresponds well to this superficial vision we have of plants. It is almost impossible for us to imagine that, deprived of eyes, nose or ears, they can possess sight, smell or hearing. As for taste or touch, it is useless to think about it. And yet they are undoubtedly endowed with meaning. And not only the five that we are attributed with, but a dozen more, of which we are completely deprived.

Plants see

Dictionaries define sight as the ability to perceive visual stimuli through the organs assigned to this function. In this sense, plants do not have eyes, but they perceive visual stimuli, especially light, at a considerable level of development and sophistication. This sense of sight is vital for plants because light is the main source of energy for them through photosynthesis. The search for light is the activity that most influences the activity and strategic behaviour of all plants.
In animals, evolution has placed the main senses (sight, hearing, smell) in a strategic position: the anterior part of the head near the brain, the sole command centre of the organism. Plants do not function at all in this way. They have evolved to avoid concentrating their strategic functions on a single space. They therefore do not have organs of sight like the eyes, but they are equipped with a multitude of hypersophisticated photoreceptors that distinguish all wavelengths of light. These photoreceptors are found in the leaves of course, but also on the stem, tendrils, vegetative apexes and even the so-called "green" wood. A plant is thus covered with a multitude of tiny eyes. Even the roots have them and are sensitive to light, to escape it.
When, in winter, some plants lose their leaves, Stefano Mancuso does not hesitate to say that they "close their eyes". They interrupt the process of photosynthesis and go to sleep, just as an animal closes its eyelids and prepares to rest.

Smells and fragrances in the form of messages

If we move on to the sense of smell, strange as it may seem, we will have to put aside all our reticence and admit that the sense of smell of plants is extremely delicate. " warns Mancuso. As with the "eyes" of plants, smell receptors are distributed throughout the plant organism. From roots to leaves, every plant consists of billions of cells with receptors for volatile substances on their surface. These substances trigger a series of signals that communicate information to the rest of the body. This is how they receive data from their environment and communicate with each other or with other organisms such as insects. For the author, all the smells exhaled by plants such as rosemary, basil, lemon or licorice are equivalent to specific messages. These are the "words" in the vocabulary of a language of which we know almost nothing.
Plants emit volatile messages to alert their fellow creatures of a danger, a threat. Attacked by a herbivorous insect, a plant will immediately exhale molecules to inform neighbouring plants so that they can relate to the danger. They will thus produce chemical molecules that can make the leaves indigestible or even poisonous to the attacker. The tomato is a specialist in this field: when attacked by a herbivorous insect, it emits large quantities of volatile substances capable of alerting other plants up to hundreds of metres away.

Don't touch the plants too much: they can smell it.

Is a plant aware of the contact caused by external objects or beings? And can it, for its part, touch an object or a being to get information from it? The author provides convincing answers to these two questions. Plants are aware that we touch them. The best known example is the mimosa leaf, which bears its learned name: Mimosa pudiqua. The sheet is sensitive and retracts as soon as you touch it. A plant shy which earned him his Latin name. Scientists are perplexed by this voluntary act, which is not at all a reflex. For a drop of water or the breath of the wind does not produce this effect. It would be a defensive strategy of the plant. Other plants use more offensive strategies. This is the case of the famous carnivorous plants that attract insects to feed on their nitrogenous components. These plants have sensors that alert them when something comes into contact with them and allow them to distinguish different types of sensations.
Examples of the sense of touch of plants are numerous in nature: climbing plants as well as all those that produce tendrils. As soon as they touch an object, they curl up to hold on to it.

Plants "hear"

If plants are endowed with the ability to hear, should we talk to them? Some people say that plants grow better when you talk to them or when you make them listen to music. These seemingly fanciful claims are not so fanciful. Animals can hear sounds in the air. These are sound waves that resonate in our eardrums. Plants do not have ears. So how can they be able to hear? They use a different sound carrier than air: the earth. To perceive sounds, plants do exactly as the Indians did in the westerns of our childhood: they listen to the sounds transmitted by the ground. The earth is indeed a conductor of such a quality that ears are useless. The sound vibrations are picked up by a multitude of plant cells with mechano-sensitive channels. All parts of the plant (in the air as well as in the soil) are covered with millions of tiny ears. This is how the roots are guided by these imperceptible sounds underground. But they themselves produce sounds as they grow. These are the "clicks" that result from the breakage of the cellulose cell walls as they grow. These characteristic sounds are "heard" by the other parts of the plant and help to organize its progress harmoniously.

Fifteen other senses

Plants would therefore be endowed with our five senses. But they also have about 15 of them, which we do not have. They are able to determine the moisture content of a site and to locate water sources to direct their roots to them. They are able to perceive gravity and the electromagnetic fields that influence their growth. As true analytical laboratories, they also have the ability to measure chemical gradients in the air or soil. Finally, they can detect dangerous chemical compounds in order to stay as far away from them as possible.

Plants communicate

Equipped with all these senses, the plant is able to communicate. Internal and external communication, the plant spends its life communicating.
Able to measure dozens of different parameters and to process considerable amounts of data, the plant orientates itself in its environment. Is it too hot, does it lack water, does it have too much? The plant adjusts its organism thanks to these sensory sensors. To transport the information, the plant has no nerves like an animal. Therefore, it cannot emit electrical signals. Instead, it uses a sophisticated vascular system that allows it to send hydraulic and chemical signals. Do the roots of an oak tree feel that there is no more water available in the soil? They will therefore send signals to the leaves alerting them to the danger so that the leaves can regulate their consumption.
Plants also communicate with others. Whether by gestural, chemical or olfactory communication, plants know how to communicate with each other. Stefano Mancuso notes how pines avoid touching their extremities so as not to hinder their growth towards the light. Plant politeness? He explains how plants recognise their relatives and protect their offspring. That they are capable of selfishness but also altruism, that they know how to establish relationships with other living beings, bacteria or insects, in order to develop. The communication of plants takes its full extent in the mechanisms of reproduction: the use of insects or small pollinating animals being the best known expression.

Can we talk about "plant intelligence"?

The association of these two words creates a form of dissonance in our ears. This is the result of millennia of misunderstanding. Because plants are immobile, because they do not have individualized organs such as the brain or the heart, because their development is slow, because none of their parts are irreplaceable, plants have always appeared to us as strangers, even preventing us from remembering that they are alive. So imagining that they are "intelligent" was until Mancuso considered a fantasy.
If intelligence is defined as the ability to solve problems, then plants are intelligent. Plants do not have eyes but yet they see, they do not have noses but they smell, they do not have ears but they hear. They don't have brains but... they are able to solve problems.
In plants, "brain functions are not separated from body functions: they coexist in every cell". For Stefano Mancuso, there is no doubt: " plants deserve to be called intelligent by right ». This is demonstrated, among other things, by their root apparatuses, which are deployed with the help of countless command centres, which together guide them like a kind of distributed intelligence that, as it grows and develops, assimilates information that is vital to their survival. « Recent advances in plant biology now make it possible to see them as organisms with a well-established ability to acquire, store, share, process and use information from their environment. "he wrote. His research in plant neurobiology focuses on understanding " how these brilliant creatures obtain [this information] and transform it into consistent behaviour ".

READ ALSO IN UP : The intelligence of trees: another world, a new look at the forest

The intelligence of plants should be an inexhaustible reservoir of bio-inspiration. Protecting this capital of life is an emergency. Every year, thousands of species of which we know nothing are disappearing, and with them, we do not know what resources. Mancuso challenges us and encourages us in his book to judge the plants closest to us. In 2008 in Switzerland, the Federal Ethics Commission for Biotechnology in the Non-Human Field (ECNH) published a document entitled The dignity of the creature in the plant kingdom ». Should we introduce, as we have done with the dignity of animals, the notion of the dignity of plants? If plants are intelligent, why shouldn't they also have rights?
Stefano Mancuso and Allessandra Viola, L'intelligence des plantes, Editions Giunti, 2013 - English translation April 2018, Albin Michel

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