The following is excerpted from Plant Intelligence and the Imaginal Realm, recently published by Inner Traditions.

The deep intelligence possessed by plants has been explored, and discussed, by many people of note over the past several centuries, including Goethe, Luther Burbank, George Washington Carver, Masanobu Fukuoka, Jagadis Bose, and the Nobel Prize-winner Barbara McClintock. Nevertheless, their research and findings have usually been dismissed, irrespective of its competence. As Brenner et al. comment about Bose (and the concept of plant intelligence in general) . . .

Bose’s overall conclusion that plants have an electromechanical pulse, a nervous system, a form of intelligence, and are capable of remembering and learning was not well received in its time. A hundred years later, concepts of plant intelligence, learning, and long-distance electrical signaling in plants have entered the mainstream literature. . . . Nevertheless, the concept of plant intelligence [still] generates a considerable amount of controversy. [1]



The discomfort among reductionists has been so extreme that, as Baluska et al. (2005) note, for a very long time, the reports of a sophisticated plant nervous system “was labeled as pseudoscience and ‘doomed’ for oblivion.” [2] Research indicating intelligence in plants, whenever it appeared, irrespective of the source, was consistently attacked by “mainstream” researchers as mystical, a romanticization of the natural world, or as anthropocentrism.

But really, when you think of it,

we have a lot more in common with a plant than a car.

Mechanomorphism—the projection onto Nature of a mechanical nature—is a lot more ridiculous than the idea of plant intelligence ever could be

As Anthony Trewavas once put it, “The use of the term ‘vegetable’ to describe unthinking or brain-dead human beings perhaps indicates the general attitude [toward plants].” [3] In consequence, most of the work by Goethe and the others has been ignored, and in many cases forgotten. Even Barbara McClintock, whose work on corn transposons eventually earned her the Nobel Prize, was ostracized for over a decade, because of the discomfort her work caused. And while her work was eventually recognized, her methodology, like that of Goethe et al., has been dismissed. As one of her colleagues once put it . . .

I respect McClintock’s work; I just don’t like her mysticism

Despite this, plants, it turns out, really are highly intelligent and yes, they do have a brain. It’s just that no one ever looked in the right place. Oh, wait! There was someone, a long time ago, who did look in the right place.

His name was Charles Darwin.

(Oops!)

Darwin commented in one of his last works, The Power of Movement in Plants, that

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. [4]



This book of Darwin’s, his second to last, has been long ignored. It contains some of the most powerful insights about plants since Goethe’s work nearly a century before. (Jagadis Bose, during the latter nineteenth and early twentieth centuries would take it considerably further.) Darwin had two genuinely deep insights that are paradigm altering: 1) that the root of the plant is in fact its brain; and 2) that the plant is using sensitive, and intelligent, analysis of it surroundings to navigate through the soil.

But Darwin’s insight was just the beginning; depth analysis of plants since the turn of the (new) millennium is finding that their brain capacity is much larger than Darwin supposed, that their neural systems are highly developed—in many instances as much as that of humans, and that they make and utilize neurotransmitters identical to our own. It is beginning to seem that they are highly intelligent—­perhaps as much or even more so than humans in some instances. (They can even perform sophisticated mathematical computations and make future plans based on extrapolations of current conditions. The mayapple, for instance, plans its growth two years in advance based on weather patterns.)

But, that can’t be true. They just sit there when we kill them

(yeah? and no matter how fast a human runs, the lion still finds him tasty.)

Increasing numbers of researchers, in a multiplicity of fields, are beginning to acknowledge that intelligence is an inevitable aspect of all self-organized systems—that sophisticated neural networks are a hallmark of life. Some researchers are becoming quite vocal in attacking what they call the “brain chauvinism” of the old-school (male) scientists who are still clasping firmly to their bosom (26A) the shreds of twentieth-century scientific certitudes. Kevin Warwick, a cyberneticist, observes succinctly that, “Comparisons (in intelligence) are usually made between characteristics that humans consider important; such a stance is of course biased and subjective in terms of the groups for whom it is being used.” [5] In other words, rationalists, who have long attacked the concept of intelligence and awareness in Nature as antirational Romantic projection, have been themselves been merely looking at and for their own reflection in the world around them—and, of course, finding the world wanting. But what especially activates their antirational subjectivity is whenever the organism in question appears to not have a brain, such as with bacteria, viruses, and most especially plants.

Plants and Perception

The old paradigm about plants, which is very common and (unfortunately) still believed by most people, is that plants are “passive entities subject to environmental forces and organisms that are designed solely for accumulation of photosynthetic products.” But as Baluska et al. continue . . .

The new view, by contrast, is that plants are dynamic and highly sensitive organisms, actively and competitively foraging for limited resources both above and below ground, and that they are also organisms which accurately compute their circumstances, use sophisticated cost-benefit analysis, and that take defined actions to mitigate and control diffuse environmental insults. Moreover, plants are also capable of a refined recognition of self and non-self and this leads to territorial behavior. This new view considers plants as information-processing organisms with complex communication throughout the individual plant. Plants are as sophisticated in behavior as animals but their potential has been masked because it operates on time scales many orders of magnitude longer than that operation in animals. . . . Owing to this lifestyle, the only long-term response to rapidly changing environments is an equally rapid adaptation; therefore, plants have developed a very robust signaling and information-processing apparatus. . . . Besides abundant interactions with the environment, plants interact with other communicative systems such as other plants, fungi, nematodes, bacteria, viruses, insects, and predatory animals. [6]



As with all self-organized systems, plants continually monitor their internal and external worlds for informational/functional shifts in the relevant fields. If they are focusing externally, once they note a shift, they work to identify its nature and meaning, and its likely impact on their functioning. Then they craft a response.

Plants continually monitor every aspect of their environment: spatial orientation; presence, absence, and identity of neighbors; disturbance; competition; predation, whether microbial, insect, or animal; composition of atmosphere; composition of soil; water presence, location, and amount; degree of incoming light; propagation, protection, and support of offspring (yes, they recognize kin); communications from other plants in their ecorange; biological oscillations, including circadian; and not only their own health but the health of the ecorange in which they live. As Anthony Trewavas comments, this “continually and specifically changes the information spectrum” to which the plants are attending.

That’s a brilliant phrase, “information spectrum,” and its deeper meanings deserve to be teased out a bit. It reflects the truth that every living organism is immersed in a bath of sensory inflows every moment of their lives. Every part of those sensory inflows contains depth information about what is going on around that organism; the sensory inflows are in fact encodings of meanings, communications from the complexity of the scenario in which the organism is embedded. And the use of the word “spectrum” is, well, brilliant. Just as light can be separated into a spectrum of colors, each with different impacts, so too the bath of sensory inflows is a spectrum of simultaneously occurring informational inputs, each of which can be teased apart and focused upon should the part of the organism that gates sensory data indicate it is important enough to do so. In one of his most insightful statements Trewavas comments that, in general, “There is no unique separate response to each signal in this complex [of informational inflows] but merely a response issued from an integration of all environmental and internal information.” [7] In other words, unless there is an informational inflow that the plant’s sensory gating mechanisms identify as crucial to respond to,

such as extensive leaf damage from spider mites which will stimulate the plant to focus more specifically

the plant normally does not use any form of linear cause and effect processing of data. It integrates the entire informational inflow that surrounds it into one holistic gestalt at each and every moment in time and generates a response that comes out of a unique, and very important, state of being.

It is actually a kind of dreaming

And not the kind of dreaming you are thinking about either

But a different kind of dreaming entirely

(It’s like the dreaming you do when you are reading this book)

That dreaming is the central core of what this book is about

It is the kind of dreaming that Goethe was engaged in

When he learned about plant metamorphosis

And Luther Burbank when he looked deep into the plant

And saw every environment its ancestors had ever lived in

And the same kind that Barbara McClintock did

When she watched individual chromosomes in corn shift their structure

It is the same state of mind that writers enter when they create worlds

It is also how Gaia dreams the world into being

And it is the kind of dreaming you can do, too, if you wish,

If you decide to walk through the doors of perception

And find out what is on the other side

As Trewavas continues, these plant responses are highly intelligent. “Given the plethora of signals that plants integrate into a response, autonomic responses do not occur. Signal perception is instead ranked according to assessments of strength and exposure.” In other words, typical sensory gating as it exists in all organisms. But then he notes, as researchers in so many other fields are now doing, that the living organism, in this instance a plant, actually chooses the optimum response from a plethora of alternatives. As he says, potential “responses can be rejected; the numbers of different environments that any wild plant experiences must be almost infinite in number. Only complex computation can fashion the optimal fitness response.” [8]



Some plants, such as sundew, are so sensitive to touch, for example, that they can detect a strand of hair weighing less than one microgram (one millionth of a gram) to which they then respond. But what is more revealing is that they can determine with great specificity what is touching them. Raindrops, a common experience in the wild, produce no response. This kind of mechanosensitivity, which is, in plants, similar to what we call our sense of touch, is used much as we use our own: The plants analyze what is touching them, determine its meaning, and craft a response. And that response many times involves rapid changes in their genetics, phenotype, and subsequent physical form. As McCormack et al. comment, “Plants perceive much more of their environment than is often apparent to the casual observer. Touch can induce profound rapid responses . . . in Arabidopsis, changes in gene expression can be seen within minutes after touch, and over 700 genes have altered transcript levels within 30 min. [9]



Many of the research papers that found a lack of intelligent response in plants, and that have been cited endlessly in the past by reductionists, were conducted in laboratories. Trewavas remarks succinctly that such results should have been expected. Laboratory studies will always misleading in this way, for wild plants live in wild not tame environments.

No such simplicity of circumstance is available to an individual wild plant, which in meeting an almost infinite variety of environmental states must construct individual responses to improve its own fitness. No genome could contain the information that would provide an autonomic response to every environmental state. And even cloned individuals do not exhibit identical responses. [10]



The only place that unintelligence, that systems of simple linear cause and effect, can reliably be found is in systems created by human beings—or in their laboratories. As Ilya Prigogine and Isabelle Stengers comment . . . .

The artificial may be deterministic and reversible. The natural contains elements of randomness and irreversibility. This leads to a new view of matter in which matter is no longer the passive substance described in the mechanistic world-view but is associated with spontaneous activity. [11]



In wild systems intelligence, free will, choice, innovation, sophisticated adaptation are inherent. These capacities in plants, as in us, are due to extremely sophisticated neural networks and are as Baluska et al., observe, “specialized for neuronal-like activities based on plant synapses.” [12] A “brain,” as we think of it, is just not necessary. Trewavas comments that

It is now known (1) that various steps in metabolism act like many Boolean compute logic gates such as AND, OR, and NOR and are termed chemical neurons, (2) that these chemical neurons can act as pattern-recognition systems, (3) that proteins can act as computational elements, and (4) that protein phosphorylation using about 1,000 protein kinases in both animals and plants provides for enormous numbers of complex elements of control, switching mechanisms and including both positive and negative feedback interactions. . . . Even in simple networks collective computational properties arose with parallel processing and extensive numbers of associative memories emerged as attractors occupying part of the network. . . . The cell in which zillions of molecular events occur at a time computes in parallel fashion, just like a brain. . . . The cellular network perceives continual environmental variation through a multiplicity of receptors. . . . Such networks learn either by increasing the synthesis of particular constituents or by changing the affinity between particular network steps by post-translational modification. Memory is simply the retention with time of the enhanced pathway of information flow and can be accessed by other pathways through cross talk. Cellular networks capable of these properties are entitled to be called intelligent. [13]



Plants, in fact, possess a highly sophisticated neural system and while it does not look like our “brain,” it really is, in actuality, a brain. In fact, once you get over brain chauvinism, it’s not all that different from our own.

The Plant Brain

It is common for people to view plants, for example a tree, as having a “head” and “feet,” the head being the tree or its canopy, the feet being the root system. But it turns out that our orientation is incorrect.

This kind of human misorientation is not uncommon. A well known environmental activist once told me, “Old growth forests are monocultures; there is very little diversity of life in them.” And many people have used that thinking to support the cutting of old-growth forests. But it turns out that he was (as are so many others) guilty of two-dimensional thinking. If you go upward, into the canopy of the forest, you will find one of the most complex and diverse ecosystems on Earth. There are plants and insects and animals there that make the diversity found in younger forests seem simplistic in comparison. And if you go into the soil surrounding those trees roots, you will find the same kind of complex community of life. Plants, in fact, construct within themselves a three-dimensional gestalt of their local space that includes not only the three- dimensional space of the rhizome world in which the root/brain exists but also of the canopy world that comes into being as the plant matures. Plants, in fact, negotiate both their form and behavior through a three-dimensional maze space—a topological surface that is continually changing in shape—that is constrained by the energy/movement of multitudes of other actors. And within those zones a diversity of life emerges that could not exist otherwise. Neither the Earth nor plants are limited to two-dimensional thinking it seems, just people.

In complex organisms the head, or anterior pole of the body, is the part that processes information, the posterior pole the part that engages in sexual reproduction and excretion of waste. From that orientation plants live with their heads in the Earth, their asses in the air. We love the smell, usually, of their reproductive organs and pick them to give to our beloveds (a highly suggestive though unconscious act). We don’t, most of us, really know plants at all.

If you can get your head around that picture, the root system of a tree being its brain, its head, and the part we normally see being its lower body, you will probably experience a sense of disorientation accompanied by nausea.

what we think of as “up,” isn’t

That, again, is the experience that accompanies the restructuring of software. It is a direct experience of how off our accepted pictures of the world generally are and just how different the world really is from what we have been taught. The plant brain does exist and it is just as elegant as our own, in many respects more so. As Frantisek Baluska et al. comment . . .

Although plants are generally immobile and lack the most obvious brain activities of animals and humans, they are not only able to show all the attributes of intelligent behavior but they are also equipped with neuronal molecules, especially synaptotagmins and glutamate/glycine-gated glutamate receptors. Recent advances in plant cell biology allowed identification of plant synapses transporting the plant-specific neurotransmitter-like molecule auxin. This suggests that synaptic communication is not limited to animals and humans but seems widespread throughout plant tissues. [14]

And as Trewavas amplifies . . .

Learning and memory are the two emergent (holistic) properties of neural networks that involve large numbers of neural cells acting in communication with one another. But, both properties originate from signal transduction processes in individual cells. Quite remarkably, the suite of molecules used in signal transduction are entirely similar between nerve cells and plant cells. . . . Learning results from the formation of new dendrites, and memory lasts as long as the newly formed dendrites themselves. The neural network is phenotypically plastic and intelligent behavior requires that plastic potential. Plant development is plastic too and is not reversible; many mature plants can be reduced to a single bud and root and regenerate to a new plant with a different structure determined by the environmental circumstances. [15]



In other words, if you take the cutting of a plant from one location and plant it in another, as the neural system of the plant develops in the soil, analyzing its surroundings all the while, it alters, as it learns, the shape and formation of emerging neural net and the plant body it develops. This, more effectively, fits it into the environment in which it is now growing. In short, plants possess a highly developed root brain which works much as ours does to analyze incoming data and generate sophisticated responses. But what is more, the plant brain that emerges always fits its functional shape to the environment in which it appears. The plant neural net, or brain, is highly plastic when compared to ours.

A unique part of the plant root, the root apex (or apices, which are the pointed ends of the root system) is a combination sensitive finger, perceiving sensory organ, and brain neuron. Each root hair, rootlet, and root section contains an apex; every root mass millions, even billions, of them. For example, a single rye plant has more than 13 million rootlets with a combined length of 680 miles. Each of the rootlets are covered with root hairs, over 14 billion of them, with a combined length of 6,600 miles. Every rootlet, every root hair, has at its end a root apex. Every root apex acts as a neuronal organ in the root system. In contrast, the human brain has approximately 86 billion neurons, about 16 billion of which are in the cerebral cortex. Plants with larger root systems, and more root hairs, can have considerably more brain neurons than the 14 billion contained in rye plants; they can even rival the human brain in the number of neurons. And when you look at the interconnected network of plant roots and micorrhizal mycelia in any discrete ecosystem, you are looking at a neural network much larger than any individual human has ever possessed.

I still remember seeing a great, ancient maple send shudder after shudder through its trunk one year—for days on end. The entire tree was undulating; I’d never seen or felt anything like it before. Some dimension of the world that I had never encountered before was intruding itself into my experience. It literally felt like the underpinnings of my world view were crumbling. It seemed as if the tree were having an epileptic seizure, something far outside my experience of trees. Then, with a great crash one day, a single giant, diseased limb came hurtling down from the canopy, at which point the shudders ceased. In a flash of insight then, I understood that trees self-prune, that they self-caretake, that I had only the barest understanding of the plant world and finally grasped Einstein’s observation that “we still do not know one thousandth of one percent of what nature has revealed to us.”

While humans and many other animals, for example, have a specific organ, the brain, which houses its neuronal tree, plants use the soil as the stratum for the neural net; they have no need for a specific organ to house their neuronal system. The numerous root apices act as one whole, ­synchronized, self-organized system, much as the neurons in our brains do. Our brain matter is, in fact, merely the soil that contains the neural net we use to process and store information. Plants use the soil itself to house their neuronal nets. This allows the root system to continue to expand outward, adding new neural extensions for as long as the plant grows.

Old growth plants then begin to take on a much different character than their younger offspring. There are states of being that only come into play with age, and with the extensive development of expanded neural fields; the neuronal structure in an ancient redwood or old growth Artemisia absinthium is different from that in younger plants . . . so are the memories and life experiences held within that neuronal structure. Plants become wise, too, as they age. We are not the only ones capable of it. You can literally feel the difference such maturity brings in encountering old growth trees—the young just don’t have it.

In addition, the leaf canopy also acts as a synchronized, self-organized perceptual organ which is highly attuned to electromagnetic fields. It can be viewed, in fact, as a crucial subcortical portion of the plant brain.

As Baluska et al. comment, the root apices

harbor brain-like units of the nervous system of plants. The number of root apices in the plant body is high, and all ‘brain units’ are interconnected via vascular strands (plant neurons) with their polarly-transported auxin (plant neurotransmitter), to form a serial (parallel) neuronal system of plants. From observation of the plant body of maize, it is obvious that the number of root apices is extremely high. . . . This feature makes the ‘serial plant brain’ extremely robust and the amount of processed information must be immense. [16]



Plant biologist Peter Barlow adds that the tips of the roots “form a multiheaded advancing front. The complete set of tips endows the plant with a collective brain, diffused over a large area, gathering, as the root system grows and develops, information” crucial to the plant’s survival. [17] And, as he continues: “One attribute of a brain, as the term is commonly understood, is that it is an organ with a definite structure and location which gathers or collects information, which was originally in the form of vibrations (heat, light, sound, chemical, mechanical, . . .) in the ambient environment and somehow transforms them into an output or response.” [18] By this definition, plants do have brains just as we do, but given their capacity to live for millennia (in the case of some aspen root systems, over 100,000 years) their neural networks can, in many instances, far exceed our own. Old growth aspen root systems can spread through as much as a hundred acres of soil creating a neural network substantially larger than Einstein’s or any other human that has ever lived. They are, sometimes, far, far more intelligent than human beings. Plants, it must be realized, possess a spectrum of neural networks, just as mammals do. Some plants possess extremely large networks, others possess smaller networks. In other words, “brain” size occurs across a considerable range, just as it does with mammals. Nevertheless, all plants are intelligent (just as are all mammals). They are all self-aware. They all engage in highly interactive social transactions with their communities.

So, that carrot?

It was murdered, yes.

For their neural networks to function, plants use virtually the same neurotransmitters we do, including the two most important: glutamate and GABA (gamma aminobutyric acid). They also utilize, as do we, acetylcholine, dopamine, serotonin, melatonin, epinephrine, norepinephrine, levodopa, indole-3-acetic acid, 5-hydroxyindole acetic acid, testosterone (and other androgens), estradiol (and other estrogens), nicotine, and a number of other neuroactive compounds. They also make use of their plant-specific neurotransmitter, auxin, which, like serotonin, for example, is synthesized from tryptophan. These transmitters are used, as they are in us, for communication within the organism and to enhance brain function.

The similarity of human and plant neural systems and the presence of identical chemical messengers within them illustrate just why the same molecular structures (e.g., morphine, cocaine, alcohol) that affect our neural nets also affect plants. Jagadis Bose, who developed some of the earliest work on plant neurobiology in the early 1900s, treated plants with a wide variety of chemicals to see what would happen. In one instance, he covered large, mature trees with a tent then chloroformed them. (The plants breathed in the chloroform through their stomata, just as they would normally breathe in air.) Once anesthetized, the trees could be uprooted and moved without going into shock. He found that morphine had the same effects on plants as that of humans, reducing the plant pulse proportionally to the dose given. Too much took the plant to the point of death, but the administration of atropine, as it would in humans, revived it. Alcohol, he found, did indeed get a plant drunk. It, as in us, induced a state of high excitation early on but as intake progressed the plant began to get depressed, and with too much it passed out.

and it had a hangover the next day

Irrespective of the chemical he used, Bose found that the plant responded identically to the human; the chemicals had the same effect on the plants nervous systems as it did the human.

This really should not be surprising. The neurochemicals in our bodies were used in every life-form on the planet long before we showed up. They predate the emergence of the human species by hundreds of millions of years. They must have been doing something all that time, you know, besides waiting for us to appear.

The vascular strands that support the plant body, giving it its rigid structure, also act as the peripheral nerve system for the plant. The plant’s neurotransmitters travel along the nerve system carrying information to the periphery, just as they do in our bodies. The plant roots engage in finely detailed analysis of their environment and communicate with the rest of the plant via neurotransmitters. The leaf canopy, as well, is taking in considerable data about the exterior world above ground. That data is sent to the root brain system, again via neurotransmitters for analysis.

GABA is present in high levels in the mammalian brain where it plays a major part in neurotransmission. It is also involved in the development of the nervous system through the promotion of neuron migration, proliferation, and differentiation. GABA strongly affects neuronal growth during cortical development, promoting DNA synthesis and cell proliferation, stimulating neurons to assemble into functional networks of axons and dendrites. It, along with auxin, plays similar roles in the formation of plant root neurons.

The plant root neurons work through the use of synapses, very similar to our own. “Moreover,” as Baluska et al. comment, “not only have neuronal molecules been found in plants but plant synapses are also present which use the same vesicular recycling processes for cell-cell communication as neuronal synapses.” [19]



The neuronal plant cells in the root exist in what is called the transition zone of the root apex. Baluska et al. note that “as cells of the transition zone are not engaged in any demanding activities, such as mitotic divisions or rapid cell elongation, they are free to focus all their resources on the acquisition, processing, and storing of information.” [20] Storing of information, that means memory. As they continue: “Smart plants can memorize stressful environmental experiences and can call upon this information to take decisions about their future activities.” [21] That is, they plan ahead.

The root apex is covered with a root cap which is designed to protect the apex and which also possesses sophisticated sensing capabilities. It screens the environment it encounters for large numbers of factors, processes the information, and alters its, and the plant’s, behavior accordingly. “As a result,” as Baluska et al. note, “roots behave almost like more active animals, performing very efficient exploratory movements in their search for oxygen, water, and ions.” [22]



Notes

1. Brenner et al., “Plant neurobiology: An integrated view of plant signaling,” 414.

2. Baluska et al., “Plant synapses: Actin-based domains for cell-to-cell communcation,” 106.

3. Trewavas, “Aspects of Plant Intelligence,” 1.

4. Charles Darwin, The Power of Movement in Plants, 573.

5. Kevin Warwick, QI, 9.

6. Baluska et al., “Neurobiological view of plants and their body plan,” in Baluska, Mancuso, Volkmann, eds., Communication in Plants, 31.

7. Trewavas, “The Green Plant as Intelligent Organism,” in Baluska, Mancuso, Volkmann, eds., Communication in Plants, 3.

8. Ibid.

9. McCormack et al., “Touch-Responsive Behaviors and Gene Expression in Plants,” in Baluska, Mancuso, Volkmann, eds., Communication in Plants, 256–67.

10. Trewavas, “The Green Plant as Intelligent Organism,” in Baluska, Mancuso, Volkmann, eds., Communication in Plants, 4.

11. Quoted in Midgley, Science as Salvation, 34.

12. Baluska et al., “Neurobiological view of plants and their body plan,” in Baluska, Mancuso, Volkmann, eds., Communication in Plants, 23.

13. Trewavas, “The Green Plant as Intelligent Organism,” in Baluska, Mancuso, Volkmann, eds., Communication in Plants, 4–5.

14. Baluska et al., “Root apices as plant command centres,” 1.

15. Trewavas, “Aspects of Plant Intelligence,” 2.

16. Baluska et al., “Neurobiological view of plants and their body plan,” in Baluska, Mancuso, Volkmann, eds., Communication in Plants, 28–29.

17. Barlow, “Darwin and the ‘Root Brain’” in Baluska, Mancuso, Volkmann, eds., Communication in Plants, 39.

18. Ibid., 48.

19. Baluska, et al., “Neurobiological view of plants and their body plan,” in Baluska, Mancuso, Volkmann, eds., Communication in Plants, 21.

20. Ibid., 27.

21. Ibid., 21.

22. Ibid., 28.

Teaser image by Michael Arrighi, courtesy of Creative Commons license.