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The Secret Life of Plants: Does Your Crop Have Feelings? Featured

Do plants really have feelings? Do plants really have feelings?


Animated vegetables like Triffids are confined to science fiction, and we have little trouble distinguishing animals from plants. However, biologists have long known that plants do sense and react in ways that resemble animals. But how much do the re-searchers really know, and can they answer the perennial question, “Do plants feel pain?”

This was a topic that interested Charles Darwin. His 1880 book The Power of Movement in Plants attempted to show how plant behavior adapted to any environment. Like others, he noted how plants were sensitive to light, gravity and touch. He was particularly interested in the radicle, the growing tip of a seedling, and suggested that plants had a nervous system: “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.”

The celebrated Indian botanist and physicist Jagadish Chandra Bose, who developed a device called a crescograph to re-cord the movement of the growing tip of a plant at high magnification, carried out further work in this area. In 1907 he published a paper on the electrophysiology of plants and showed that they produced an electrical potential in response to contact or damage. The obvious conclusion was that they possessed the same sort of nervous system as animals.

The amazing-but-true phenomena are regularly wheeled out by nature lovers as a sign of the unity of all living things, and even more regularly used to taunt vegetarians that cabbages have feelings too.

The flagship for plant feelings is the “sensitive plant,” Mimosa pudica, a tropical plant that reacts to being touched by folding up its leaves. This seems to be a defense against heavy rainstorms, and it shows that plants are capable of animal-like reactions to their surroundings. The Venus flytrap, which snaps shut when trigger hairs are touched, is a more specialized example, and both plants have been studied intensively.

However, in the 1960s, scientific work on plant feelings was overshadowed in the media by less rigorous work with more immediate appeal. If Bose could attach instruments to plants, so could others. Cleve Backster, an ex-CIA operative and chair-man of the Research and Instrument Committee of the Academy for Scientific Interrogation, was inspired by Bose’s work to hook up a polygraph to plant leaves.

Backster claimed that not only did plants respond to damage, but they also responded to the threat of damage, and even other plants or animals being damaged nearby.

Not one to be left out, L. Ron Hubbard created headlines about “screaming tomatoes” in 1968. He attached an e-meter, the Scientologists’ favorite electronic device for measuring electrical resistance, to plant leaves. The media were intrigued. While much of the coverage was frivolous, with interviewers like Alan Whicker asking Hubbard if rose pruning should be allowed, he garnered plenty of publicity for his research and was featured in Life magazine.

The Secret Life of Plants, by Peter Tomkins and Christopher Bird, which covers various plant phenomena, was a bestseller in 1973; Stevie Wonder released his soundtrack to the subsequent documentary as an album. Lyall Watson’s Supernature, also a bestseller in 1973, helped popularize the same findings.

The cumulative effect was to lodge screaming plants firmly in the public consciousness. The “amazing but true” phenomena are regularly wheeled out by nature lovers as a sign of the unity of all living things, and even more regularly used to taunt vegetarians that cabbages have feelings too.

However, the world of science was moving away from the idea of plant pain well before Backster. Darwin’s suggestion that the radicle acted like a brain was rejected by plant physiologists at the time, and The Power of Movement in Plants did not attract a following. Scientists from Cornell University replicated Backster’s experimental setup in 1975, but failed to find any evidence for the “primary perception” he had claimed.

In the meantime, we have learned much more about how plant senses work. Plants do not have anything that resembles a central nervous system, which rules out feeling in the traditional sense. But they do have bundle-sheath cells running along their veins, and these carry the electrical potential measured by Bose. The potential drives the Mimosa pudica’s reaction and many others. Many plants have phototropins, chemicals sensitive to blue light, which can trigger a reaction to lengthen one side of a stem so that flowers turn to face the sun. A different mechanism reacts to red light and allows plants to sense day and night.

Some of the mechanisms involved turn out to be highly sophisticated, and get translated into headlines like the BBC’s “Plants Can Think And Remember” or the Daily Mail’s “Plants Can Talk, Say Scientists.” That’s the sound of analogies being overstretched. My computer is not really thinking while the hourglass symbol is displayed, doesn’t play chess intelligently and doesn’t remember the files stored on it.

There are still plenty of mysteries around how plants respond and communicate. They signal to each other by emitting ethylene gas and hormones, and there are indications that roots emit and respond to sounds. They can “smell” airborne chemicals and “taste” with their roots, sensing and reacting to other plants nearby. Plants really do have many of the capabilities you would associate with animals, but they work by very different means.

They are life, you might say, but not life as we know it.

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The Mythbusters test some of the theories referenced in the above article.
Last modified on Friday, 12 July 2013 18:28

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