Plant intelligence is a field of plant biology which aims to understand how plants process the information they obtain from their environment. Plant intelligence has been defined as "any type of intentional and flexible behavior that is beneficial and enables the organism to achieve its goal".
Plant neurobiology is a subfield of plant intelligence research that claims plants possess abilities associated with cognition including anticipation, decision making, learning, and memory. Terminology used in plant neurobiology is rejected by the majority of plant scientists as misleading, as plants do not possess consciousness or neurons, thus the term plant gnosophysiology is infrequently used. Most plant scientists tend to avoid using the term "intelligence" to refer to plants in their published research, despite the rise of the term in popular science writing.
History
Early research
In 1811, James Perchard Tupper authored An Essay on the Probability of Sensation in Vegetables which argued that plants possess a low form of sensation, have sensitivity, and potentially have a nervous system. It was believed that thinkers like Tupper who believed in plant sensitivity credited God, who kindly designed all organisms with purpose.
The notion that plants are capable of feeling emotions was first recorded in 1848, when Gustav Fechner, an experimental psychologist, suggested that plants are capable of emotions and that one could promote healthy growth with talk, attention, attitude, and affection.Heidelberger, Michael. (2004). Nature From Within: Gustav Theodor Fechner and his Psychophysical Worldview. University of Pittsburgh Press. p. 54. Federico Delpino wrote about plant intelligence in 1867.
The idea of cognition in plants was explored by Charles Darwin in 1880 in the book The Power of Movement in Plants, co-authored with his son Francis. Using a neurological metaphor, he described the sensitivity of plant roots in proposing that the tip of roots acts like the brain of some lower animals. This involves reacting to sensation in order to determine their next movement.Darwin, C. (1880). The Power of Movement in Plants. London: John Murray. Darwin Online : "The course pursued by the radicle in penetrating the ground must be determined by the tip; hence it has acquired such diverse kinds of sensitiveness. It is hardly an exaggeration to say that the tip of the radicle thus endowed, 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." Darwin's "root-brain hypothesis" influenced those in the field of plant neurobiology many years later.
John Ellor Taylor in his 1884 book The Sagacity and Morality of Plants argued that plants are conscious agents. He says that, "there can be no life absolutely without psychological action — that the latter is the result of the former." He believed that plants possess a similar trait to instinct in animals which is gaining experience and passing down those experiences to descendants.
In 1900, ornithologist Thomas G. Gentry authored Intelligence in Plants and Animals which argued that plants have consciousness. Literary scholar Ed Folsom described it as "an exhaustive investigation of how such animals as bees, ants, worms and buzzards, as well as all kinds of plants, display intelligence and thus have souls".
Captain Arthur Smith in the early 1900s authored the first article on "plant consciousness". In his article, Smith blurred the lines between plants and animals by pointing out the "sensibility" of plants, like animals, to outside stimuli as a form of consciousness. Smith argued that the brain, which plants lack, is not necessary for consciousness, since animals like Protozoa and Coelenterata lack it but still are labeled as conscious. Also, Smith defined intelligence as the ability to change behaviors based on different situations, as seen in the Mimosa when it responds to light touch, shadows, and darkness.
In 1905, Rev. Charles Fletcher Argyll Saxby authored a pamphlet, Do Plants Think? Some speculations concerning a neurology and psychology of plants.
Maurice Maeterlinck wrote about the intelligence of flowers in 1907.
Royal Dixon in his 1914 book, The Human Side of Plants argued that plants are sentient and have minds and souls.
Jagadish Chandra Bose Jagadish Chandra Bose invented various devices and instruments to measure electrical responses in plants.V. A Shepard cited in Alexander Volkov. (2012). Plant Electrophysiology: Methods and Cell Electrophysiology. Springer. p. 12. "Bose began by applying delicate instrumentation he had invented in his semiconductor research to deliver electrical stimuli and record electrical responses from various plant parts... He discovered that both living animal and plant tissues exhibited a diminution of sensitivity after continuous stimulation, recovery after rest, a 'staircase' or summation of electrical effects following mechanical stimulation, abolition of current flow after applying poisons and reduced sensitivity at low temperature." Bose is considered an important forerunner of plant neurobiology by proponents of plant cognition.
According to biologist Patrick Geddes "In his investigations on response in general Bose had found that even ordinary plants and their different organs were sensitive— exhibiting, under mechanical or other stimuli, an electric response, indicative of excitation."Geddes, Patrick. (1920). The Life and Work of Sir Jagadis C. Bose. Longmans, Green & Company. p. 120 One visitor to his laboratory, the vegetarian playwright George Bernard Shaw, was intensely disturbed upon witnessing a demonstration in which a cabbage had "convulsions" as it boiled to death.Geddes, Patrick. (1920). The Life and Work of Sir Jagadis C. Bose. Longmans, Green & Company. p. 146
Bose was the author of The Nervous Mechanism of Plants, published in 1926. Karl F. Kellerman, Associate Chief of the Bureau of Plant Industry, United States Department of Agriculture criticized Bose's interpretation of the results from his experiments, stating that he failed to prove the conclusions from his reports that plants feel pain. Kellerman commented that "Sir Jagadar passed an electric current through plants, and his instruments recorded a break in the current. Such variations in resistance to electric current are found even when passing a current through dead matter".
Cleve Backster
In the 1960s Cleve Backster, an interrogation specialist with the CIA, conducted research that led him to believe that plants can feel and respond to emotions and intents from other organisms including humans. Backster's interest in the subject began in February 1966 when he tried to measure the rate at which water rises from a philodendron's root into its leaves. Because a polygraph or "lie detector" can measure electrical resistance, which would alter when the plant was watered, he attached a polygraph to one of the plant's leaves. Backster stated that, to his immense surprise, "the tracing began to show a pattern typical of the response you get when you subject a human to emotional stimulation of short duration".Backster, Cleve. (2003). Primary Perception: Biocommunication with Plants, Living Foods, and Human Cells. White Rose Millennium Press. His ideas about primary perception (plants responding to emotions and intents) became known as the "Backster effect".
In 1975, K. A. Horowitz, D. C. Lewis and E. L. Gasteiger published an article in Science giving their results when repeating one of Backster's effectsplant response to the killing of brine shrimp in boiling water. The researchers grounded the plants to reduce electrical interference and rinsed them to remove dust particles. As a control, three of five pipettes contained brine shrimp while the remaining two only had water; the pipettes were delivered to the boiling water at random. This investigation used a total of 60 brine shrimp deliveries to boiling water while Backster's had used 13. Positive correlations did not occur at a rate great enough to be considered statistically significant. Other controlled experiments that attempted to replicate Backster's findings also produced negative results.Galston, Arthur W; Slayman, Clifford L. Plant Sensitivity and Sensation. In George Ogden Abell, Barry Singer. (1981). Science and the Paranormal: Probing the Existence of the Supernatural. Junction Books. pp. 40-55. Schwebs, Ursula. (1973). Do Plants Have Feelings? Harpers. pp. 75-76Chedd, Graham. (1975). AAAS takes on Emotional Plants. New Scientist. 13 February. pp. 400-401Neher, Andrew. (2011). Paranormal and Transcendental Experience: A Psychological Examination. Dover Publications. pp. 155-156.
Botanist Arthur Galston and physiologist Clifford L. Slayman who investigated Backster's claims wrote:
There is no objective scientific evidence for the existence of such complex behaviour in plants. The recent spate of popular literature on "plant consciousness" appears to have been triggered by "experiments" with a lie detector, subsequently reported and embellished in a book called The Secret Life of Plants. Unfortunately, when scientists in the discipline of plant physiology attempted to repeat the experiments, using either identical or improved equipment, the results were uniformly negative. Further investigation has shown that the original observations probably arose from defective measuring procedures.
John M. Kmetz noted that the Backster effect was based on observations of only seven plants, which nobody including Backster was able to replicate.
The television show MythBusters also performed experiments (season 4, episode 18, 2006) to test the concept. The tests involved connecting plants to a polygraph galvanometer and employing actual and imagined harm upon the plants or upon others in the plants' vicinity. The galvanometer showed a reaction about one third of the time. The experimenters, who were in the room with the plant, posited that the vibrations of their actions or the room itself could have affected the polygraph. After isolating the plant, the polygraph showed a response slightly less than one third of the time. Later experiments with an EEG failed to detect anything. The show concluded that the results were not repeatable, and that the theory was not true.
Backster's research was cited in the pseudoscientific book The Secret Life of Plants in 1973. Whilst the book captured public attention it severely damaged the credibility of the field of plant intelligence. Philosopher Yogi H. Hendlin noted that the book's "combination of haphazard, panpsychist metaphysical speculations and unmethodical citizen science stigmatised legitimate progressive plant research, alongside the era's new-age pseudoscience, tarring the discipline's serious inquiry".
Dorothy Retallack In 1973, Dorothy Retallack authored The Sound of Music and Plants. In the book, Retallack records experiments she conducted at Colorado Women's College on applying different music to plants in controlled chambers. After about 20 experiments, she stated that the plants died in response to acid rock, had no response to country music, and flourished under classical music and jazz. Retallack was ecstatic to find out that she and the plants had overlapping taste in music.
Despite Retallack's pride in her experiments, the experiments were described as pseudoscientific and poorly designed as there was a lack of control for factors such as humidity, light and water. Also, Retallack did not have scientific definitions for genres of music. Professors and researchers from Colorado Women's College expressed anger and embarrassment over the experiments. Nonetheless, Retallack's work had a lasting impact, as attempts to replicate her experiment are still ongoing to this day.
Modern research