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plant perception (a.k.a. the Backster effect)

Plants are living things with cellulose cell walls, lacking nervous or sensory organs. Animals do not have cellulose cell walls but do have nervous or sensory organs. Animals are sentient; plants are not. That is, animals can experience pain, pleasure, and various emotions. A brain and nervous system are necessary for sentience; plants don't have brains or nervous systems. Plants react to physical and chemical stimuli, but there is no justification for claiming that plants are aware of these reactions, that they are self-conscious or conscious beings. Plants have DNA and have evolved by natural and artificial selection. Some plant adaptations can seem "intelligent," but calling plants intelligent, or claiming that there is a "plant neurobiology," is to speak metaphorically and is little more than a gimmick aimed at getting attention and perhaps some grant money.

It would never occur to a plant or animal physiologist to test plants for consciousness or ESP because their knowledge would be sufficient to rule out the possibility of plants having feelings or perceptions on the order of human feeling or perception. In layman's terms, plants don't have brains or anything similar to brains. One may as well speak of bacteria or viruses as having brains and nervous systems.

However, a person completely ignorant of plant and animal science has not only tested plants for perception and feeling, he claims that he has scientific proof that plants experience a wide range of emotions and thoughts. He also claims that plants can read human minds. His name is Cleve Backster and he published his research in the International Journal of Parapsychology ("Evidence of a Primary Perception in Plant Life," vol. 10, no. 4, Winter 1968, pp. 329-348). He tested his plants on a polygraph machine and found that plants react to thoughts and threats.

Dr. Backster claims to have a D.Sc. in Complementary Medicine from Medicina Alternativa (1996). He has parlayed his doctorate into a position at the California Institute for Human Science Graduate School and Research Center, an unaccredited institution founded by Dr. Hiroshi Motoyama for the study of "the human being as tridimensional." Dr. Motoyama is said to be a scientist and Shinto priest who "has awakened to states of consciousness that enable him to see beyond the limits of space and time."*

Backster's claims were refuted by Horowitz, Lewis, and Gasteiger (1975) and Kmetz (1977). Kmetz summarized the case against Backster in an article for the Skeptical Inquirer in 1978. Backster had not used proper controls in doing his study. When controls were used, no detection of plant reaction to thoughts or threats could be found. These researchers found that the cause of the polygraph contours could have been due to a number of factors, including static electricity, movement in the room, changes in humidity, etc.

Nevertheless, Backster has become the darling of several occult, parapsychological and pseudoscientific notions. His work has been cited in defense of dowsing, various forms of energy healing, remote viewing,* and the Silva mind control program (now known as the Silva method). In 1995, Backster was invited to address the Silva International Convention in Laredo, Texas. Nearly thirty years after his original "discovery," he is still telling the same story. It is a very revealing story and worth repeating. It shows his curious nature, as well as his apparent ignorance of the dangers of confirmation bias and self-deception. Backster clearly does not understand why scientists use controls in causal studies.

the "lab" & the Eureka! experience

Backster tells us that it was on February 2, 1966, in his "lab" in New York City that he did his first plant experiment. His "lab" was not a science lab. In fact, it wasn't much of a lab at all in the beginning. It was just a place where he conducted training in the use of the polygraph. There was a plant in the room. He recalls the following:

For whatever reason, it occurred to me that it would be interesting to see how long it took the water to get from the root area of this plant, all the way up this long trunk and out and down to the leaves.

After doing a saturation watering of the plant, I thought, "Well gee whiz, I've got a lot of polygraph equipment around; let me hook the galvanic skin response section of the polygraph onto the leaf.*

The galvanic skin response (GSR) section of the polygraph measures the resistance of the skin to a small electrical current. Defenders of the polygraph think that galvanic skin responses are related to anxiety, and therefore to truthfulness. The theory is that when a person lies they are anxious and the amount of sweat increases slightly but measurably. As sweat increases, the resistance to electrical current decreases. Clearly, Backster is a very curious individual. A less inquisitive person would probably not care how long it would take water to get from the root to the leaves in an office plant. Not only did Backster care but he put his polygraph equipment to use as a measuring device. He reasoned as follows:

I felt that as the contaminated water came up the trunk and down into the leaf that the leaf becoming more saturated and a better conductor it would give me the rising time of the water....I would be able to get that on the polygraph chart tracing.

Why would the polygraph indicate this? Because, he says, he was using a "wheatstone bridge circuit that is designed to measure resistance changes." Presumably, resistance changes would be picked up by the polygraph as the water reached the leaf. He predicted that the resistance would slowly drop and the tracings on his polygraph paper would rise as the water reached the leaf. Instead, the opposite happened, which, he says, "amazed me a little bit."

Apparently, he moved the electrodes and saw that the contour of the polygraph chart was "the contour of a human being tested, reacting when you are asking a question that could get them in trouble." Backster claims that he then gave up his interest in measuring how long it takes water to get from the roots to the leaves of his plant. He says he believed that the plant was trying "to show me people-like reactions." He claims his next thought was: "What can I do that will be a threat to the well-being of the plant, similar to the fact that a relevant question regarding a crime could be a threat to a person taking a polygraph test if they're lying?" This is truly is amazing. The contour of the graph triggered in him an immediate identification of the plant with one of his subjects. Until that moment, apparently, Backster had never suspected that the plants in his office were just like people and would respond similarly. Why he thought of threatening the plant isn't quite clear. I doubt that he threatened his human subjects. It also is not quite clear why the response to a threat to one's well-being would result in the same kind of response as being caught in a lie. At least Backster seems not to have considered seriously the notion that the plant might try to deceive him.

Backster says he tried for 13 minutes and 55 seconds to get a reaction out of the plant by doing such things as dipping a leaf in warm coffee, but he got no response. A less devoted inquisitor might have given up and gone home at this point, but not Backster. He concluded that the plant seemed like it was bored. Then, he had his Eureka! experience: "I know what I am going to do: I am going to burn that plant leaf, that very leaf that's attached to the polygraph." Now, why he would burn the leaf isn't clear, since burning it would (a) eliminate its moisture, making measurement of galvanic response impossible, and (b) it might damage his equipment attached to the leaf. Anyway, he tells us that there was a problem with carrying out his plan: he didn't have any matches. He claims, however, that while standing there some five feet from the plant the polygraph "went into a wild agitation." Rather than conclude that maybe the water finally got to the leaf or some other natural event was causing the polygraph needle movements, Backster became convinced that the plant was reading his mind and was reacting to his intent to burn it. This is indeed an interesting inference to make at this point. He gives no indication that he even considered that there might be other possible explanations for the movement of his polygraph. This may strike some readers as a good thing, that a gifted mind immediately grasps the truth. But actually this is a bad thing because your intuition could be wrong. What is very curious is that after more than thirty years of experiments, there is still no evidence that Backster and his many supporters see the importance of using controls in their studies of alleged plant perception. 

Anyway, to return to the original experiment: Backster admits that he committed a bit of petty larceny in the name of science: he went to another office, went into a secretary's desk drawer and retrieved some matches. When he got back to his experiment, he lit a match, but careful and observant scientist that he was, he realized that the machine was so agitated he wouldn't be able to measure any additional agitation. So, he left the room. When he returned "the thing just evened right out again, which really rounded it out and gave me a very, very high quality observation." What he meant by "a very, very high quality observation" is not clear. Backster's true genius is exhibited in his final remark on the remarkable experiment:

Now when my partner in the polygraph school we were running at the time came in, he was able to do the same thing also, as long as he intended to burn the plant leaf. If he pretended to burn the plant leaf, it wouldn't react.

It could tell the difference between pretending you are going to, compared to when you actually intend to do it, which is quite interesting in itself from a plant psychology standpoint.*

Plant psychology? I think Backster invented it that night. Had he just a smattering of understanding regarding the importance of using controls for studies which try to establish causality, he might have proceeded differently. The first step is to clearly define what you are testing and what each step in the procedure consists of. Backster and his partner don't have a clear notion of the difference between intending to burn the plant and pretending to be intending to burn the plant. Next, it might have occurred to them that there might be a better way to measure electrical current in plants than using a polygraph. They might have consulted with some experts and set up an experiment with proper equipment. Once they clarified what they were testing and how they would test it, they might have done twenty runs with the secretary doing the intending or pretending, them not knowing which, and them collecting the polygraph data. They would tell a third party which runs indicated pretending and which runs indicated intending. The third party would compare their claims with the secretary's data. That third party would also make sure that the polygraphers wouldn't be able to see what the secretary was doing during the experiment, lest they be influenced by something in her behavior. Then, just to be sure that it wasn't some movement the secretary made when she intended to burn the plant that caused the polygraph reaction, she should be made to make exactly the same movements when she intended and when she pretended to burn the plant. He should have done several trials with several different plants. And he probably should not have watered his plant just before doing the experiment. He should have known that moisture or humidity changes would affect the GSR readings. The fact is that Backster has never done anything like a controlled experiment and is no closer today than he was in 1966 to understanding why his polygraph made the contours it did when it was attached to his plant. Backster's admirers can truthfully say that his experiment has been repeated thousands of times around the world. Unfortunately, repeatability justifies claiming an outcome is probably true only if the original experiment was done properly.

sowing and reaping

Backster's claims have been publicized and supported by several people with qualifications and knowledge equal to his own: journalist Peter Tompkins and gardener Christopher O. Bird authored The Secret Life of Plants first published in 1973, a presentation of the work of Backster and other "scientists" which allegedly proves that plants perceive telepathically and experience emotions such as fear and love. Bird is the author of Modern Vegetable Gardening and Tompkins has several "secrets" books: Secrets of the Great Pyramid (1997), The Secret Life of Nature: Living in Harmony With the Hidden World of Nature Spirits from Fairies to Quarks (1997) and Secrets of the Soil: New Solutions for Restoring Our Planet (1998).

Another supporter and expositor of Backster's work is Robert B. Stone, Ph.D., member of Mensa, and author of The Secret Life of Your Cells published in 1994. Stone is also the author of the Silva Method (Jose Silva's mind control and self-healing program) and the Silva Method: Unlocking the Genius Within. Stone and Silva authored one book together: You the Healer. However, if one searches the literature of science, one searches in vain for support for the notion that plants are telepathic and feel emotions.

Despite the lack of scientific support for the notion of plant perception, the idea is accepted by many as not only true but as having been verified by numerous scientific studies! In fact, the power of plants to understand human thought by "reading" our "bioenergetic fields" is known among parapsychologists as the Backster effect.

Typical of the testimonials in defense of Backster's claims are the following. Notice how they echo the claim that Backster's experiment has been duplicated many times by many different people. Notice, too, that like good storytellers these advocates embellish the tale with some interesting exaggerations. None of these testimonials, however, mentions the critical studies that both failed to verify Backster's claims and also explained why his studies were flawed.

Cleve Backster used a polygraph (lie-detector) to test plants, attaching electrodes to the leaves. By recording electrical impulses he found the plants to be extremely sensitive to his thoughts, particularly thoughts that threatened their well-being. Backster also observed a reaction in a plant when even the smallest cells were killed near it. He noted that they have a kind of memory, reacting to someone who earlier had done harm to another plant nearby: in a line-up of anonymous people the plant could pick out the one who had performed the act (John Van Mater, theosophist).*

Cleve Backster was also famous, notorious in fact, and had been since about 1968 when he first claimed that plants have primary perceptions which can sense human thoughts and respond to them. This was the same as saying that PLANTS have sentient consciousness, are telepathic, and can process non-physical information. This, of course, absolutely shocked, angered and horrified scientists of all kinds, and Backster was pilloried in the media -- much to the enjoyment of hard-core parapsychologists who, back then, had nothing good to say about him.* To help correct this dismal rejection of Backster, it wasn't until the late 1980s that neurobiologists discovered and confirmed that plants do possess "primary perceptions" because they have "rudimentary neural nets."* [This claim from Ingo Swann is pure codswallop. Neurobiologists do not study plants and you will search in vain through the annals of neurobiological literature for verification of the Backster effect.]

....map dowsing has just as simple an explanation as on-site dowsing. Map dowsing seems to be related to what is sometimes called the "Backster Effect." Backster is a lie detector specialist and what he did was to attach a galvanic skin response device to the top leaf of a plant. This device measures the electrical resistance of the skin. He then watered the plant, fully expecting to measure how long it would take for the water to reach the leaf and change its resistance. Instead the lie detector immediately indicated, what would be a happy effect in humans. This puzzled him so he decided to traumatize the plant by burning, a leaf. The plant showed a fear response on the lie detector as soon as he had this thought. Backster's experiments have been duplicated thousands of times by many persons using many variations and have been well publicized on TV and in many books (Walt Woods, map dowser and author of the 20-page booklet Letter to Robin: A Mini Course in Pendulum Dowsing).

Backster's work in the late '60s and early '70s was an important impetus for the best selling The Secret Life of Plants by Peter Tompkins and Christopher Bird. In the '80s, his work was chronicled by Robert Stone in The Secret Life of Your Cells. His research journey started with the 1966 almost accidental rediscovery that plants are sentient and respond to the spontaneous emotions and strongly expressed intentions of relevant humans. (J. Chandra Bose* of India had demonstrated a similar principle in the early part of the 20th century.) Using an instrument to measure galvanic skin responses (GSR), a part of his polygraph or lie detector stock-in-trade, Backster attempted to determine whether it would measure the moment of rehydration of a plant whose roots were freshly watered. It did not but to his surprise, the GSR meter registered his threat to burn the plant leaf when he spontaneously thought of the idea....

Over the last thirty years literally hundreds of experiments have proved the existence of this biocommunication known as the "Backster Effect." My own personal participation in one of these experiments left me without a doubt that a culture of yogurt in a shielded cage showed extraordinary reactions to feeling that were stirred up in me and two female colleagues as we discussed controversial gender and power issues. Interestingly, the yogurt did not react to periods of intellectual discussion about the same issues; it only became agitated when our comments were charged with emotion (Paul Von Ward, MPA and M.S., researcher and writer in the fields of "consciousness and frontier science").*

In 1969 Marcel [Joseph Vogel] gave a course in creativity for engineers at IBM. It was at this time that he read an article in Argosy magazine entitled “Do Plants Have Emotions?” about the work of polygraph expert Cleve Backster into the responsiveness of plants to human interaction. Despite initial rejection of the concept of human-plant communication, he decided to explore these strange claims.

He was able to duplicate the Backster effect of using plants as transducers for bio-energetic fields that the human mind releases, demonstrating that plants respond to thought. He used split leaf philodendrons connected to a Wheatstone Bridge that would compare a known resistance to an unknown resistance. He learned that when he released his breath slowly there was virtually no response from the plant. When he pulsed his breath through the nostrils, as he held a thought in mind, the plant would respond dramatically. It was also found that these fields, linked to the action of breath and thought, do not have a significant time domain to them. The responsiveness of the plants to thought was also the same whether eight inches away, eight feet, or eight thousand miles! Based on the results of the experiments the inverse square law does not apply to thought. This was the beginning of Marcel’s transformation from being a purely rational scientist to becoming a spiritual or mystical scientist.

Basically it was found that plants respond more to the thought of being cut, burned, or torn than to the actual act. He discovered that if he tore a leaf from one plant a second plant would respond, but only if he was paying attention to it. The plants seemed to be mirroring his own mental responses. He concluded that the plants were acting like batteries, storing the energy of his thoughts and intentions. He said of these experiments: “I learned that there is energy connected with thought. Thought can be pulsed and the energy connected with it becomes coherent and has a laser-like power.”(Rumi Da, purveyor of fine crystals).*

In the seventies, a best-selling book called The Secret Life of Plants presented scientific research from around the world that explored plant intelligence. The chapter which made the biggest impression on me described a retired policeman in New York City, Cleve Backster, who trained people how to use lie detectors. As a lark, he hooked up his plants to a polygraph so he could monitor their responses.

One day, Backster approached his Dracaena Massangeana with a lighted match and acted as if he were going to burn it. Not only did the plant go wild on the graph but every other plant in the place did, too. He could hardly believe it. Continuing to experiment, he discovered that the plants responded to his thoughts even when he was miles away. One day, on the New Jersey Turnpike, he decided to let them know, through thought, that he was on his way home. When he arrived, he found that the plants had responded excitedly on the graph at the exact time he was communicating to them. Proximity was not a factor in their ability to sense him!

Everyone can develop this skill and ability. We all have it within us. All we have to do is acknowledge the possibility of it being true and then proceed with an open mind and heart (Judith Handlesman, spiritual gardener and vegetarian).*

Clearly, Backster has his followers and they think he has done fundamental and extraordinary work in science. Why hasn't he been awarded his Nobel Prize? Why does nearly the entire scientific community ignore him? The answer should be obvious. Nevertheless, Backster continues his work at the Backster Research Center in San Diego, California, where he claims to be able to demonstrate that his plants respond to his loving thoughts and even obey his thought commands.

Ingo by jingo!

One of Backster's greatest admirers and defenders is remote viewing promoter Ingo Swann ("Remote Viewing - The Real Story"). Swann is the one quoted above who falsely claims that Backster's work was vindicated in the 1980s by neurobiologists when it was discovered that plants have neural networks. In 1971, according to Swann, Backster invited him to his plant lab and polygraph school. There Ingo claims he, too, made the polygraph needle hooked up to the plant "go haywire" when he thought of burning the plant with a match. He was able to repeat the event several times and then he couldn't get a response. Swann recalls the event and comes up with what he and Backster think must be the logical conclusion. Of course, neither one of them thinks they could be mistaken or deceived. It does not occur to either of them that they had better set up some controls.

"What does THAT mean," I asked. "You tell me." Then a very eerie thought occurred to me, so astonishing that it caused goosebumps. "Do you mean," I asked, "that it has LEARNED that I'm not serious about really burning its leaf? So that it now knows it need not be alarmed."

Backster smiled. "YOU said it, I didn't. Try another kind of harmful thought." So I thought of putting acid in the plant's pot. Bingo! But the same "learning curve" soon repeated itself. Now I already understood in my own "reality" that plants are sentient and telepathic, as all plant lovers know who talk to their plants. But that plants could LEARN to recognize between true and artificial human intent came as a thunderbolt! Among all this astonishment I came across the concept of the "learning curve" which ultimately was to play THE feature role in the development of remote viewing.

But Backster was moving on. "Do you think you could influence some kind of metal or chemical?" "I don't know how to influence anything. But I could try." So for several weeks I went to the Times Square lab to try to zap metals and chemicals -- and the march of what I was unknowingly being sucked into moved into October, 1971.*

This kind of amateur approach to experiment and naive reinforcement of speculations as if they were facts established by incontrovertible evidence is typical of Backster and his supporters. A knowledgeable scientist would never be taken in by such rudimentary reasoning and speculation. But a scientifically ignorant person could easily be duped by these experiments.

the Backster effect and primitive religion

Jim Cranford is another defender of Backster, whom he sees as providing proof that animistic religions truly did involve communicating with vegetation.

Although similar experiments [to Backster's] have been repeated thousands of times, all over the world, for more than 15 years, we have failed to grasp the implications. Part of the problem is that Backster is not a "scientist" and those guys don't like to admit that anyone else knows anything. That's pride and arrogance at its worst, but not so unusual in the laboratory. Even the rest of us find it hard to believe that the "primitives" were actually communicating with their plants through rituals and sacrifice. We simply refuse to believe that there could be any "intelligence" around here but us, while we live in a world smarter than us at every turn. It is obvious that our collective view of primitive religion is in need of some revision.

At least Cranford recognizes that Backster is not a scientist. "Those guys" would require controls when they do causal studies.

Backster and theosophy

Another advocate of Backster's ideas is theosophist John Van Mater, Jr., who thinks that Backster's work supports the notion that

...there is a life force, a cosmic energy surrounding living things, shared by all kingdoms including the human....Nature is a great brotherhood of beings, a symbiosis on many levels, most of it beyond our detection and ordinary understanding. The vegetable kingdom is an essential layer of the living planet's vitality or prana, helping to provide in its metabolism a breathing, intelligent organ that produces and regulates the atmosphere as well as transfers energy into the biosphere. Plants are also a link in the chain of beings, in which each kingdom or level needs the others in order to function and evolve. (See "Our Intelligent Companions, the Plants," John Van Mater, Jr., Sunrise magazine, April/May 1987 published by Theosophical University Press.)

Thus, Backster's shoddy science is brought in to support metaphysical notions to go along with his support for dowsing, energy healing, telepathy, remote viewing and who knows what else.

scientific support?

Although mainstream science has shunned Backster's claims about telepathic plants and their "primary perception," Earthpulse.com, a New Age UFO/Environmentalist site that sells "frontier science" books, allegedly found a botanist named Richard M. Klein (1923-1997) from the University of Vermont to provide a blurb for The Secret Life of Plants.

If I can't 'get inside a plant' or 'feel emanations' from a plant and don't know anyone else who can, that doesn't detract one whit from the possibility that some people can and do....

Truer words were never spoke. Too bad Dr. Klein didn't teach Mr. Backster how to conduct a proper double-blind controlled study. After all, Backster may have finally found a proper use for the polygraph.

[new] real science of plant communication

For information about plant sensing and communication that is based on science, one might read the work of biologist Richard Karban. See, for example, Plant Sensing and Communication (University of Chicago Press, 2015). There you will read such things as "a flowering weed—mousear cress (Arabidopsis thaliana)—can sense the particular chewing noise of its most common caterpillar predator and adjust its chemical defenses in response." For those who are wondering, Dr. Karban did not use a polygraph machine to determine plant sensitivities. [/new]

*note1: It is interesting that John Kmetz had a different reading of the media. Kmetz writes: "It is unfortunate that the popular press has taken Backster's experiments and presented the results to the public in such a way that many people now believe plants can do something that, in fact, they cannot. The press, for the most part, never mentions that articles on the Backster effect are based on observations of only seven plants. Perhaps they need to be reminded, again, that they are making exaggerated claims from an experiment that no one, including Backster, by his own refusal to do so, has been able to replicate."

 *note2: Sir Jagadis Chundra Bose was a Bengali scientist and admirer of the French vitalist Henri Bergson

further reading


Galston, A. W. and C. L. Slayman. (1979). The not-so-secret life of plants. American Scientist, 67 337-344.

Horowitz, K. A., D.C. Lewis, and E. L. Gasteiger. 1975. Plant primary perception. Science 189: 478-480.

Kmetz, J. M. 1977. A study of primary perception in plants and animal life. Journal of the American Society for Psychical Research 71(2): 157-170.

Kmetz, John M. 1978. Plant perception. The Skeptical Inquirer. Spring/Summer, 57-61.


Cleve Backster from 1995 Silva International Convention

Phytodynamics and Plant Difference by Gunalan Nadarajan

New functions for electrical signals in plants

Smarty Plants: Inside the World's Only Plant-Intelligence Lab

TED talk, Stefano Mancuso


UCD prof: Plants can eavesdrop, sense danger in their environment By Kathy Keatley Garvey, Davis Enterprise, August 12, 2015

Last updated 07-Nov-2015

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