The Question of Intelligence and Sentience in Plants

Is intelligence “what is needed to solve problems” or does it require a brain?

Tony Fearnside, M.Sc., OAM, 2015.


In 1973, the publication of The Secret Life of Plants by Peter Tompkins and Timothy Bird occasioned much controversy. Appearing at a time when New Ageism was strong, the book was a “best seller” in USA and inspired a popular documentary film of the same name (Paramount 1979). One of the book’s controversial claims was that plants may be sentient despite their lack of a nervous system and a brain.

The book opened with a report on “Cleve” Backster, a former interrogation specialist for the CIA and his experiments with plants using a polygraph or lie detector in the 1960s (Grover Cleveland “Cleve” Backster, Jr (1924 – 2013)). These were widely reported in the media but were rejected by the scientific community. His book Primary Perception — Biocommunication with Plants, Foods, and Human Cells (2003) described his work with plants, including attaching a polygraph to an indoor plant (Dracaena massangeana) in his office. Backster reported that the plant registered a reaction on the polygraph when he had thoughts of injuring it and when a live shrimp was put into boiling water in the next room. Controlled experiments that attempted to replicate Backster’s findings failed, and the “Primary Perception” theory was not accepted since it did not follow a scientific method (eg. at the 141st annual meeting of the American Association for the Advancement of Science in 2011, the panel of biologists found the claim unsupportable).

Backster’s theory was a subject of an episode of the television show Mythbusters. After all human and environmental stimuli that could alter the results were removed, they tried to reproduce Backster’s experiments with the Dracaena massangeana plant. After obtaining negative results, they performed a final experiment using an EEG instrument (more sensitive than a polygraph) connecting it to a plant to check whether it would react to eggs being catapulted randomly into boiling water. The instrument registered no change in the plant and the myth was considered busted! (

However, critics had overlooked a characteristic of plants which was reported in chapter two of The Secret Life of Plants. Marcel Vogel, a researcher at IBM who could be described as empathetic to plants, was asked to give a course to IBM staff members on creativity. He set out to demonstrate a machine with similar capabilities to Bachster’s polygraph and divided the class into three groups; none of the students got results but Vogel did. He concluded that plants could respond to a person’s intentions if there was some sort of a bond between the person and the plant.

A deliberate attempt to see if Backster’s results could be replicated using the equivalent of a galvanic skin response[1] was made by theosophist Steven Guth and David Beale in 2007 and 2011.   David, an electronics inventor developed a ‘materials analyzer’ that sends out and receives modulating patterned waves. It was adapted to present results similar to the GSR machines. Antenna and receiver plates were placed near plants and results were recorded as Steven meditated and sent feelings of love and appreciation to the plants. Garden trees responded slowly. Potted geraniums cuttings tended to give good results. A further experiment was conducted by moving a geranium over a dowsing water line – the plant responded to the line. Steven observed that plants appear to react much like cats, “One needs to get and hold their attention. Responses are not always what one expects.” Steven and David have placed their work, with photographs on the following web site: .

Controversy re-awakened in 2007 as a result of an article by six plant scientists in Trends in Plant Science (2006) that proposed a new field of inquiry “plant neurobiology”. They argued that this name was justified by the sophisticated nature of plant responses to environmental variables which could not be explained using accepted genetic and biochemical definitions. Systems of signalling in plants had been found that are analogous to systems in animals – plants exhibited intelligence. The Society for Plant Neurobiology had held its first meeting in 2005. After criticism from other plant scientists, the society was re-named the Society for Plant Signalling and Behaviour and its journal became Plant Signalling and Behaviour.

Associate professor Monica Gagliano, from the Centre for Evolutionary Biology, University of Western Australia, working at the International Laboratory of Plant Neurobiology near Florence experimented with seedlings of the sensitive plant (Mimosa pudica). She used protocols for testing habituation in animals by repeatedly dropping containers with the seedlings from a height of 15 centimetres every five seconds. At first, the seedlings responded as they do to touch, by “folding up” but after a while they had “learned” that this was unnecessary. 28 days later the plants “remembered” what they had learned. She said “Brains and neurons are a sophisticated solution, but are not a necessary requirement for learning.” Her paper was rejected by 10 scientific journals, not because they doubted the results or the methodology, but they could not agree to use her terminology, to which she replied that it was necessary to use similar terminology so that plant and animal behaviour could be compared (the paper was eventually published in Oecologia).

It is not surprising that the “plant neurobiologists” have turned to information science for definitions and terminology which are broader and concepts that are easier to apply than those of physiology.

So, are we getting closer to finally refuting or accepting the existence of sentience in plants as propounded by eastern sages, and by CW Leadbeater and others who possessed a degree of clairvoyance? Probably not, but much more is now known of what was previously the “secret” life of plants and therefore of the claims to their having some sort of intelligence or “sentience”.

Some things that plants do (plant behaviour)

The following describes some aspects of above-ground plant movements or “behaviour” in vascular or higher plants (land plants that have lignified tissues (xylem) for conducting water and minerals through the plant and a specialised non-lignified tissue (phloem) to conduct products of photosynthesis). Vascular plants include gymnosperms (conifers and cycads) and angiosperms (flowering plants). Mosses, yeasts (and other single-celled organisms) are not considered here. (

Firstly, let’s consider the oft repeated anonymous observation, “We live in a definition based reality, held in place by peer review.” In the case of plant studies much of the discussion and controversy centres on the terminology and definitions. Thus “behaviour” can be taken to be reactions to stimuli. In animals, reactions are usually characterised by movement that is readily observed while most reactions to stimuli in plants are much, much slower. If we remember that plants are unable to move we begin see that this greatly influences and helps to explain their slower responses, and their different ways of signalling, etc. Arising from this we can also argue that plants have advantages over animals in many respects (eg, a plant can lose 90% of its structure and still survive, while having a brain as in higher animals would be a disadvantage as foragers could easily destroy the plants ability to defend itself). Perhaps we humans should be more humble and abandon our feeling of superiority brought about by our (apparent) ability to out-think species in the animal and plant kingdoms. Meanwhile remembering that living entities take steps to pass on their genetic material and consume materials to provide the necessary energy. (In so doing, animals generally consume materials to provide energy and plants generally generate their own energy sources.)

In plants, vegetative growth is the period of growth between germination and flowering and the following table indicates the different forms of growth that are recognised in vascular plants. source:

Seeds absorb moisture sufficient to generate energy for growth to begin (germination).
Plants move in response to environmental stimuli where movement is related to the direction of the stimulus (tropisms eg, geotropism in roots, movements caused by wind).
Plant movements in response to light which are not tropic: photomorphogenesis eg the diurnal movement of sunflowers.
Movements by plants in response to environmental stimuli where movement is not related to the direction of the stimulus (nastic movements eg, the Venus fly trap, and Mimosa pudica [sensitive plant]).
Time dependent movements eg, closing of flowers, or leaves at night (Circadian responses).
Processes that occur during vegetative growth, ie, between germination and flowering are referred to as general growth.
Growth associated with reproduction, including pollination and pollination aids, flowering, fertilisation, fruiting and seed disposal. Eg, Rafflesia is a genus of parasitic plants[2] that attracts insects at night by emitting (to us) an unattractive stink.

In the case of the insectivorous plant, the Venus Fly Trap (Dionaea spp) an insect crawling on the plant’s leaf will bend a single hair but nothing happens … until a second hair is bent by the insect, whereupon the leaf closes quickly and catches it. Is this a form of intelligence, since the plant knows the difference between a single bend and a second bend? (A single bend could be caused in many ways but potential prey will cause two bends.) (

In the parasitic plant, dodder (Cuscuta spp) seeds sprout at or near the surface of the soil. Although germination can occur without a host, it has to reach a green plant quickly and is adapted to grow towards the nearby plants by following chemosensory clues. If a host plant is not reached within 5 to 10 days, the seedling will die. Before a host plant is reached, the dodder relies on its food reserves. It has been demonstrated that dodder plants “hunt” their preferred victims (eg, tomato plants) by responding selectively to different volatile airborne compounds emitted by their potential hosts. (

Another fascinating case is that of the parasitic pitcher plant, Nepenthes hemsleyana. The large pitcher that this plant possesses has been shown to attract bats by reflecting sounds that enable bats to more easily locate the pitcher plant amongst other plants through echolocation. When the bats roost above the pitcher plant in considerable numbers, their droppings provide nutrients for the plant. (

So far in this section, we have considered above-ground movements which are far easier to observe than below-ground movements. Moreover, plant scientists have begun to move from studying single plants or even parts of a plant to groups of plants and thence to plants in the landscape, no doubt benefiting from advances in technology. (In contrast to clairvoyants who tend to move from landscapes to groups of plants to individual plants or trees.)

The below-ground behaviour of plants can be even more intriguing than their above-ground behaviour. Recent work has shown that roots somehow avoid overcrowding with their own species, take action to avoid other species that may be competitors and to seek out organisms that may be helpful, such as symbiotic fungi or bacteria.

The growing tip of a root (or radicle) is generally regarded as comprising a protective but sensitive growing tip, followed by a region of rapidly dividing cells (meristem), then a transition zone and an elongation zone. Plant neurobiologists have now proposed that the transition zone is in fact a “nerve centre” that controls or directs growth and that this is a form of intelligence (Ananthaswamy, 2014). In addition to tropic movements (in response to gravity, lack of light, moisture, and penetrability) plant roots can respond to chemicals (nitrogen, salt, phosphorus, toxins, microbes and chemical signals from neighbouring plants. (Pollan, 2013.)

Are plants sentient, showing intelligence?

The question of whether plants are sentient entities with intelligence (perhaps how plants decide what, and how, to do things) has long been controversial, and events in the past 40 years have been no exception. Before closing, let us consider a few definitions of “sentience” which in general usage is the ability to feel, perceive, or experience subjectively.

The on-line psychology dictionary defines sentience as: 1. The most primitive and simple form of cognition. 2. The state of being sentient. And “Sentience consists of being aware of stimuli without interpreting them. (

In Eastern philosophy, sentience is a metaphysical quality of all things, and calls for care and respect. The concept is central to the philosophy of animal rights because sentience is necessary for the ability to suffer: (

It seems certain that those who want to believe that science is getting closer to demonstrating sentience in plants because scientists are becoming more able to demonstrate forms of plant intelligence, will readily accept that science is indeed closing in on proving that plants are intelligent, sentient beings. While the naysayers will remain unconvinced.


Anil Ananthaswamy New Scientist 6 December 2014.

Gagliano, M., Renton, M.S., Depczynski, M.R., Mancuso, S. 2014,Experience teaches plants to learn faster and forget slower in environments where it matters’, Oecologia, 175, 1, pp. 63-72.

Michael Pollan The New Yorker 23 December 2013.


The quoted web sites were accessed in early July 2015.


[1] A measure of changes in emotional arousal recorded by attaching electrodes to any part of the skin and recording changes in moment-to-moment perspiration and related autonomic nervous system activity


[2]   Including Rafflesia arnoldii, said to be the largest flower in the world.

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