Wildlife & Biodiversity

Listen... plants too speak

As early as in 1880, Charles Darwin demonstrated that plants could sense light, moisture, gravity, pressure and possessed several other qualities. Over the years, many scientists have proved that plants are sentient beings and move and respond to sensation. The subject is still controversial among the scientific community. Monica Gagliano is research associate professor of evolutionary ecology and former fellow of the Australian Research Council who has pioneered a brand-new research field of plant bioacoustics. In her latest book, 'Thus Spoke the Plant: A Remarkable Journey of Groundbreaking Scientific Discoveries and Personal Encounters with Plants', she, for the first time, has experimentally demonstrated that plants emit their own voices and detect and respond to the sounds of their environments. In these excerpts, Gagliano writes about how the pea plant responds to acoustic vibrations to locate water

By Monica Gagliano
Published: Wednesday 02 January 2019
Paintings: Raj Kumar Singh


Oryngham means thank you for listening in the language of the plants. It is not a word, as we humans understand it, because its meaning cannot be spoken—nor can it be heard. However, we can experience it by feeling with our bodies and listening to what our ears cannot hear. When we learn to listen to plants without the need to hear them speak, a language that we have forgotten emerges; it is a language beyond words, one that does not wander or pretend or mislead. It is a language that conveys its rich and meaningful expression by bypassing the household of our mind and directly connecting one spirit to another. This language belongs to plants, and so do these stories.

In general, organisms use various kinds of information transmitted by smells, sounds, lights, or magnetic fields in order to make good choices and avoid fatal errors. Based on this idea and as instructed by Ayahuma, I designed the experiments with the peas in the maze to test how roots choose the direction that correctly leads them to water, depending on the cues available. Particularly, could the roots of the young peas sense the acoustic vibrations generated by water moving underground or inside pipes? Could they use the sound of water alone to detect and find its source, when no actual water was available in close vicinity?

To answer this, I wrapped a sealed, soft plastic pipe through which water was constantly flowing around the base of one side of the maze, but the water itself was never directly accessible to the plants. Then I compared the choices roots made in these mazes to those they made growing in mazes where the soil was kept moist by actual water contained in the small plastic tray attached at the base of one side of the maze, hence producing a moisture gradient.

The sensory world of plants contains a complex assortment of informational components; they are extremely good at resolving an enormous influx of information by prioritizing cues that support the overall most beneficial decision

What emerged was exciting. In mazes in which actual water was available, the vast majority of seedlings followed the moisture gradient and directed their root to the side where the water source was located. But seedlings were equally successful at locating the water source when they grew in mazes in which they had no direct access to water—no moisture gradient—but only the sound of water circulating inside the sealed pipes. And if both a moisture gradient and the sound of water were made available in the same maze, what would the young plants choose? They chose the obvious—with no hesitation, the vast majority of seedlings grew their roots into the side of the upside-down Y-maze that led them straight to water! While moisture or acoustic cues are equally useful in helping roots locate water, their relevance and usefulness to a plant depend on the context. What the peas were really showing me was that they choose which cue is most advantageous in what circumstance.

From this perspective, my ecological and logical interpretation was that sound may enable peas to roughly detect the presence of water at a distance and, conceivably, to establish the most direct and sensible route to that source before any soil moisture is encountered. An analogy might be a bubbling watercourse in the distance or water coursing through underground fissures. Once accessible, however, it is the moisture gradient in the soil that helps them home in on their target more accurately and pinpoint the exact location of the water source. Clearly, the sensory world of plants contains a more complex assortment of informational components than what I had presented them with and, as they would show me next, they are extremely good at resolving an enormous influx of information by prioritizing cues that support the overall most beneficial decision. 


The next step in my research was to establish whether the peas were really responding to the sound of water or were simply growing toward any source of noise regardless of what the nature of the sound actually was. This was important to see just how selective and attuned they were to an ecologically relevant and rewarding sound. In animal ecology, this question is commonly addressed by playback experiments, a widely used technique in which natural or synthetic acoustic stimuli are broadcast and the response of individuals noted. I applied this approach to the young peas and found something that, at first, puzzled me—the seedlings directed their roots away from the recorded sound of water. I had attached a vibration speaker directly to one of the black plastic pots at the base of the maze. The speaker was then connected to a small MP3 player, which played the recorded sound of water in some mazes or broadcast either computer-generated white noise or silence in others. Regardless of the sound treatment I applied, none of the seedlings had access to actual water. What I found was that the majority of seedlings grew away from the side of the maze where I had attached the sound equipment, regardless of the sound playing. In fact, they avoided that side of the maze even when I played them silence! It seemed as if the seedlings were repelled by the speakers themselves. Because speakers contain small magnets, and plants are known to orientate their root systems in response to natural magnetic fields (such as gravity) as well as artificial ones, I started to suspect that perhaps the sound equipment emitted a electromagnetic (EM) field that, while imperceptible to me, was tangible enough to be sensed and avoided by the young roots.

I excitedly emailed the school of physics that housed the BioMagnetics research group, a specialized lab equipped with state-of-the-art magnetic measurement facilities to investigate the role of magnetism in biological systems, explaining that I was conducting some greenhouse experiments on the acoustic abilities of plants and that I had just stumbled onto something potentially interesting: “I think my peas are sensing the EM field emitted by my sound equipment.” It was April 2. A couple of days later, I received a reply that opened, “Hi Monica, to be honest, if I got your email a day earlier I would have just thought it was a April Fools joke.”

We had never before considered the possibility that human-altered soundscapes and acoustic pollution could be issues of potentially vital importance to plants. By prioritizing cues that supported growth, the peas spoke of responsibility

Although I discovered later that measuring EM emissions was not particularly hard, I waited for four months for my colleague to take a look at the speakers and MP3 players, as he had agreed to do. The task remained on his permanent to-do list, and after too many broken promises and countless postponements, I decided to improvise. I equipped myself with a portable low-frequency analyzer (or gaussmeter), and off I went. I measured the magnetic emissions from the sound equipment when it was turned off and compared it with the readings made when the sound equipment was turned on and playing any of the sounds I had used in the experiment with the peas. And what a surprise! When turned on, the sound equipment (the speakers and MP3 player) did produce measureable levels of magnetic emissions that could be detected within a five-centimeter radius around the source—this range happened to correspond almost exactly to the dimensions of the black plastic pot the speaker was attached to, thus making a highly localized disturbance obvious at one foot of the maze.

Trivial from a human perspective, the range of influence was absolutely relevant to the roots in the space they occupied inside the maze, and they had demonstrated this accordingly through their behavior. This was a brilliant find, of course, but the disturbing influence of the magnetic field emitted by the sound equipment now posed an unexpected complication in my attempt to discover whether roots responded selectively to the sound of water. Or so it seemed. Over the years, I had learned that seemingly problematic issues that materialize unpredictably and demand a change in existing plans can feel frustrating, but they often bear immensely productive insights and opportunities if I am prepared to stay open to alternatives. So after putting up with some initial frustration, I moved into the next phase of the research and presented the seedlings with a new choice—one between the monsters Scylla and Charybdis, so to speak.

On their epic journey through the maze, the pea seedlings reminded me of Odysseus, who, in Homer’s Odyssey, had to negotiate his memorable passage between the deadly clutches of Scylla and Charybdis, the two immortal monsters inhabiting either side of a narrow strait. In this new phase of the research, the young plants, like the Homeric hero, were to face a choice between two evils. I attached a speaker and MP3 player to each foot of the maze, one side playing the sound of water and the other side playing either white noise or silence—thus experimentally standardizing the strong repulsive effect of the sound equipment. Now that the magnetic interference was originating from both sides of the maze and could not be avoided, could the peas face what they were avoiding and choose what was most needed, namely water?

Caught between two equally unpleasant alternatives, the peas did exactly what was most appropriate, given the circumstances. Availing themselves of the other cues present in their immediate environment, the vast majority of seedlings extended their roots toward the recorded sound of water, when the player on the other side of the maze was broadcasting silence. The preference was not as strong when the other side broadcast white noise, but the recorded sound of water was still more attractive than the white noise.

Of course, this confirmed that plants preferentially moved toward the sound of water, a previously unknown phenomenon, and yet this finding of their “hearing” abilities should not come as a surprise. Over their evolutionary history, plants would have had millennia to evolve this ability to listen to and discriminate between vibrations of various kinds and then respond to those sounds that carried some meaning to them. For example, sounds produced by a running stream would have been highly relevant to a broad range of plant species and beneficial to their survival. Similarly, it was not totally surprising to see that the ability of the seedlings to clearly detect the recorded sound of water was somewhat reduced by the presence of white noise. The two sounds would have bumped into each other inside the maze, resulting in acoustic interference.

Paradoxically, the peas had made the most appropriate choice—if they had grown their roots toward the sound of water, they would have found only the magnetic disturbance and no actual water

This kind of masking effect has been observed in animal systems. From studies of birds, bats, and squirrels, to name a few, we know that white noise can interfere with an animal’s ability to receive and respond to particular relevant sounds and, consequently, can make it trickier for the animal to carry on everyday business effectively. What was striking about this finding, however, was that we had never before considered the possibility that human-altered soundscapes and acoustic pollution could be issues of potentially vital importance to plants.

By prioritizing cues that supported growth, the peas spoke of responsibility. “Responsibility is that which you are moving toward,” the plants have told me. “It is not a moral obligation, but rather the actual movement that supports the expression of care.” Inside the maze, the young pea roots had revealed an unwavering commitment to making the choice that nurtures and supports life—in this case, by finding water. “We are both living on the same earth, and we are both after the same water,” they have said.

In making their choices, the young plants were also reiterating the fundamental fact that we, humans, need the same things to flourish as plants and all life on the planet. We all have the same choices to make, choices that concern the well-being of the whole. And, ultimately, all choices are inescapably about the well-being of the whole; they differ only in the quality of their movement—some move us all toward a state of planetary vitality and health, and some away from it. Just the same, they carry us all inexorably toward the circumstances that we sow, and therefore, it seems essential to care for what is planted.

It is, then, the quality of our actions that tells the story of who we are and where we are going. Unfortunately, many of our current actions are violent, and we are living in the delusion that we can distance and guard ourselves from their consequences, as if our well-being is separate from that of the whole. Well, we cannot. We cannot because the notion that there are independent objects, each fighting for dear life in a Darwinian struggle of existence, is a lazy and archaic conjecture that does not do justice to contemporary scientific findings. There are no conflicting opponents, even when two organisms appear to have mutually exclusive properties; there is only the remarkable play of one nature displayed across a palette of rainbow colors. However, until we see ourselves inhabiting a world of polarities, we can only perceive ourselves in conflict with the whole—and our neurotic violence keeps chasing and biting at our own figurative tail.

At this crucial juncture in the evolutionary history of the planet and all living species, the circumstances are asking us to dream ourselves beyond the discordant format of a polarized reality and forward to more supportive futures

From this partial perspective, it is inevitable that the fact that our well-being is inseparable from environmental integrity generates such an unbearable tension in our society. We approach this tension by making violence permissible, so that we may justify actions that are carrying the whole to where no one actually wants to go. Instead, we should resolve our core blindness, acquiring the lucidity to see that the dynamic movement of existence is a fundamental state of communion and, hence, acting in ways that can only be beneficial to the whole— existence itself. We can opt for a reality woven together by the threads of continuity or endure the illusory belief that the world is split into an interminable succession of polarities and keep facing conflicting, even paradoxical, circumstances. This does not need to be, and choices that seem contradictory need not be so either.

To make some sense of this, I had to go back to the peas in the maze. By moving away from the sound of water emanating from a speaker at one foot of the maze, the peas in my experiment made what seemed an incongruous choice—plants surely want water no matter what, so why move away from the sound of it? As if knowing more than the appearances alluded to, the young peas made the choice that was required and moved away from trouble by, somewhat, staying at it! In the scenario they found themselves in, they selected to avoid the disturbing, possibly damaging, effects of the magnetic field produced by the sound equipment, even if that meant moving away from what was desired, namely water. In order to keep themselves safe from the harm of magnetic disturbance, they accepted the fact that water had to be found elsewhere or in some other way.

Paradoxically, the peas had made the most appropriate choice—if they had grown their roots toward the sound of water, they would have found only the magnetic disturbance and no actual water. In other words, the young plants selected something that may not be immediately beneficial but ultimately gives them a better chance of survival, rather than choosing what seemed to provide the desirable outcome, despite its disastrous consequences. By attending to what was asked by the circumstances with responsibility, the peas had effectively moved toward that which supports and protects care in the long run.

To me, the peas’ behavior inside the maze was a great lesson in the kind of responsibility the plants had spoken of to me earlier—ultimately, a choice is as good as the level of integrity we can bring to it, and it is integrity within the actions that reveals us and that ultimately defines us. Are we able to make the choice that is required and move away from our global environmental crisis by standing for what we must? Human prosperity is not in conflict with the prosperity of other species and the planet; on the contrary, thriving abundance is made-with, cocreated with others in a continuity of exchanges and sharings. In this continuity, we have no conflict to resolve and no riddle to be solved. We only have choices to make.

Like the peas in the maze, can we move away from what injures, even if this means moving away from what we think is most wanted? In order to keep the Earth and all her living species (including ourselves) safe from the threats posed by environmental deterioration, climate change, and mass extinction, are we able to accept the fact that human behavior has to find other ways of being? The faulty thinking stopping us from making the most appropriate choice is prolonging our destructive impact on the planet and, hence, ensuring that we may experience only conflict and destruction. At this crucial juncture in the evolutionary history of the planet and all living species, the circumstances are asking us to dream ourselves beyond the discordant format of a polarized reality and forward to more supportive futures.

Just like the peas in the maze, it is our conduct toward releasing the knot of the current eco-cultural tangle that reveals us in the end. And while the deafening sound of too many words still echoes between here and there, right and wrong, from life to death and back again, it is in the silent quality of our actions that the genuine spirit and kind heart of humanity is revealed. And it is then when alternate possibilities, which seem too far off, become so close; from the space in the middle, these choices are separated by only a thin pane of glass.

(From Thus Spoke the Plant: A Remarkable Journey of Groundbreaking Scientific Discoveries and Personal Encounters with Plants by Monica Gagliano, published by North Atlantic Books, copyright © 2018 by Monica Gagliano. Reprinted by permission of publisher)

'Plants have a lot more than five senses'
Monica Gagliano's claims on plant consciousness and intelligence have received an equal amount of attention and criticism. But the evolutionary ecologist says her claims are based on experiments and scientific data and that the scientific community may have to reckon with intelligent organisms independent of the traditional brain and nervous system model. Edited excerpts from an interview with SNIGDHA DAS

By training, you are an animal ecologist who has worked with small tropical fish of the Great Barrier Reef. How did you develop interest in bioacoustics and plant cognition?

It wasn't just one thing that inspired me. But once I had a different experience as I was doing my work with my fish. I realised that I don't want to kill and sacrifice my animals anymore for science. Because of this personal, ethical and moral dilemma, I started wondering how I can change my science to make it more compassionate. And I ended up turning to plants, almost by chance. As I embarked on that journey, I received a lot of support, not only from the academia or humans but from the plants themselves. And the book is all about that journey.

You describe the book as a phytobiography—a book "about" plants and "by" plants—where you are "a listener who filters out personal noise to hear plants speak, who engages in active dialog with these nonhuman intelligences". Is it possible for a lay person to hear plants speak? Unless that can happen, people mind find the idea unpalatable.

Of course, it's very much possible. But it depends on how we want to see them speak and what do we mean when we say "something is speaking to us". If we are restricting the definition to the use of words as humans do, then plants do not speak. In fact, going by this definition, nothing except the human speaks. This anthropocentric view is actually blocking us from seeing, hearing and appreciating the others, any non-human animals or other forms of life. But if anybody out there is willing to hear them speak, they will. We are animals, and by nature attuned to our environment, most of which is made of plants. So it's important to communicate with them, in whichever way, so that we know how to co-exist and co-survive. The kind of ecological mess that we are in today is because of denying that relationship.

You have mentioned in the book that to open this plant teacher-human student dialogue, you followed "the dieta, a time during which I was to ingest the plant regularly while in isolation, observing total sexual abstinence and an uninspiring diet of unseasoned vegetables and rice. So I drank the concoction made from her bark that night—and the following night too—as Socoba (a tropical rainforest tree also known as bellacocaspi or Himatanthus sucuuba) swiftly aligned with my present and quietly befriended my past". How does a lay person begin this process of communication?

There is no one way to it. Every individual needs to find their own way. But its just like starting a relationship with humans. We enjoy communicating with certain people, because we like them. Then there are those who we do not even like talking to. Those who grow plants or are close to plants know how to read them, because they observe them all the time. So, first, you need to get over the notion of what a plant should or should not be doing. Then you should have the ability to listen to others. But above all, you should be silent enough to allow your mind and body to observe and understand what they are trying to say. Use empathy to establish that connection. But again, it's true for all relationships, isn't it?

Tell us more about the process of dieta you followed to interact with the Socoba tree.

This process belongs to the South American shamanic tradition. It comes from the Amazon. Of course, it is one of the many processes they use to interact with plant spirits. The dieta requires you to put yourself in isolation, so that you are not distracted by anything else around you. It would be the same when you go for a retreat where you meditate. The only difference is that in the dieta you are either ingesting or bathing in the concoction made from the bark or leaves of the plant. The purpose is to get prepared to hear these "others" inside you. But just like meditation, it requires guidance. After a while, of course, you would be able to practice it for yourself and you would be in your meditation all the time.

You have said in the book that you had dreamt of the exact hut in the lowlands of Peru where you practised dieta, when you were back home in Australia. This sounds a little odd!

I have no idea how that happened, but that's the truth. What I know is they were not just dreams. I had three of those dreams, and they have always been about the same place and person. When I woke up after the third dream I knew that the place was real. So, I went to Google images to find out if such a place was out there. To my surprise, amid the varied images I found the image of the hut, the person and a sketch of the direction to locate it.

You describe you field of work as plant cognitive ecology. You also say plants do not have neurons. How do plants learn and remember things? How can you say for sure that their behaviour is not mechanistic but intelligent.

It's again about definition of words. Cognition does not have anything to do with the brain. Cognition in itself means "to know"—it's the process of knowing. And there are different ways of arriving at it, which can be from perception to language or thinking and imagining. It involves learning and memory. But there is nothing here that says an organism needs to have a brain to be cognitive. Even the world "intelligence" means to choose between things; it does not talk about brain.

Now we have data to prove this in scientific terms. We have data that shows plants are not only able to communicate with each other, but are also able to learn, remember and take decisions. All these are part of the cognitive realm. Making decision and learning requires an ability to choose between things, which is the definition of intelligence. Hence these organisms are intelligent. It's just that they have a decentralised approach of doing things. Most are failing to acknowledge this because they use humans as the gold standard; they think you are intelligent if you have the brain and neuros like humans. But the data compiled from plants and several other species who have the decentralised approach of doing things, contradicts this idea. This calls for a revision of several theories that define intelligent organisms. So, it's an exciting time for everyone involved, not just people working on plants and animals, but also for people working on human brain.

Of the five senses in humans, which one did you find the strongest in plants? Is the awareness and sentience in plants different from those in animals?

Plants have a lot more than five senses. As far as awareness and sentience is concerned, we are struggling to answer that question. Probably because, we do not know what that means for all forms of life. But more than the difference, it's important to understand the underlying links that unifies all.

There has been an increase in literature on plant behaviour in the last few years. What could be the reason behind this?

This increase in interest is not only among scientists but also among philosophers and artists. For centuries plants were being treated as objects. But in the past few decades, there is a growing conversation about whether we have the right to abuse the plants as we please; do we have the right to cut forest just because we want progress. They are now being treated as subjects. This is an welcome change in attitude. We are evolving as a more caring and compassionate culture. This can help save the planet.

What developments do you see in this field, say, the next decade?

I just moved to the University of Sydney, where I am setting up a new laboratory, which will focus on biological intelligence as a whole, and the plants, of course, would be the part of the story. And I would continue working with the plants and exploring their decision-making and choice abilities. I would also like to explore if morality has meaning in the conversation about plants.

(This article was first published in Down To Earth's January 1-15 print edition)

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