A few months ago at Hearing International we did a discussion of how you can hear plants grow……. Strange things are now found among plants. It has been discovered that plants can actually tell if predators are after them bugs, animals and humans! This is the story of how plants might hear, feel, smell or otherwise detect that they are being used as food and how they fend off these predators as well as warn their friends and relatives of this impending danger. Of course, these warnings have been going on since the beginning of time, but we are just finding out about how plants protect themselves from predators and the effects that this protection might have on humans: Could plants (our food) be sending and receiving auditory messages of impending danger?
Most of us will recall that there have been rumblings for a long time that plants really prefer Classical Music to Rock n’ Roll. Could it be that plants really prefer Mozart and Beethoven to the Rolling Stones or Kiss? According to the experts plants grow better, are healthier when the classics are played routinely in areas where they are growing. Wine makers play classical for their grapevines, making better wine in Mantalcino Italy. In states where marijuana is legal, the classics are played to achieve better and larger plants. Others have found that plants grow toward classical music and away from Rock n’ Roll. While logical based upon anecdotal evidence, plant or animal physiologists would not test plants for consciousness or ESP because their academic knowledge rules out the possibility of plants having feelings or perceptions on the level of humans. In layman’s terms, plants don’t have ears or brains or anything similar to anatomical auditory systems. To scientists would be as absurd as bacteria or viruses as having brains and nervous systems. While these mechanisms have developed over millions of years, the real evidence of plant communication is only a few decades old, but in this short time the concept of plants warning other plants of predators and having protective mechanisms has moved from a surprising discovery to total skepticism and now due to meticulous, controlled research back into the forefront of plant research.
In the Beginning….
The story of this interesting phenomenon really begins with a former C.I.A. polygraph expert named Cleve Backster. Probably bored in his office one day in 1966, Backster, on a whim, hooked up a galvanometer to the leaf of a dracaena houseplant that he kept in his office. To his astonishment, Backster found that simply by imagining the dracaena being set on fire he could make it rouse the needle of the polygraph machine register a surge of electrical activity suggesting that the plant felt stress. “Could the plant have been reading his mind?” the authors ask. “Backster felt like running into the street and shouting to the world, ‘Plants can think!’ ” The publication in 1968 of Backster’s initial findings elicited a strongly skeptical response from the scientific community. However, they generated wide public interest following the description of his experiments in the bestseller The Secret Life of Plants by Peter Tomkins and Christopher Bird, published in 1973. The book was heavily criticized by scientists for promoting pseudoscientific claims, it documented controversial experiments claiming to reveal unusual phenomena regarding plants such as plant sentience and discusses various philosophies and progressive farming methods based on these findings. In the years immediately following publication, amateurs and scientists alike attempted to replicate what became known as the ‘Backster effect’, testing the claim that plants respond to human thought, and particularly intention to harm them.
Two studies published in 1983 demonstrated that willow trees, poplars and sugar maples can warn each other about insect attacks: Intact, undamaged trees near ones that are infested with hungry bugs begin pumping out bug-repelling chemicals to ward off attack. They somehow know what their neighbors are experiencing, and react to it. The shocking truth was that a brainless tree could send, receive and interpret messages of impending danger. McGowan (2013) presents that “The first few “talking tree” papers quickly were shot down as statistically flawed or too artificial, irrelevant to the real-world war between plants and bugs. Research ground to a halt. But the science of plant communication is now staging a comeback. Rigorous, carefully controlled experiments are overcoming those early criticisms with repeated testing in labs, forests and fields. It’s now well established that when bugs chew leaves, plants respond by releasing volatile organic compounds into the air.” It’s now well established that when bugs chew leaves, plants respond by releasing volatile organic compounds into the air. Andrews (2011) reports one research project, where scientists took note of when the first gypsy moth larvae landed on a mature oak tree that resided in a grove with other oaks. By analyzing the chemistry of the mature oak tree’s leaves, they were able to determine that within a very short period of time, the tree had added a bitter tannin to all of its leaves. The tannin made the tree an unattractive lunch option for the gypsy moth larvae. But what was more astounding was that all the other oak trees in the grove changed the chemistry of their leaves, too, making them unappetizing as well. Recent studies of plant communication confirm that other plants detect these airborne signals and ramp up their production of chemical weapons or other defense mechanisms in response. The debate is no longer whether plants can sense one another’s biochemical messages — they can — but about why and how they do it. The answer could have big implications: Farmers might be able to use the information to improve crop resistance to pests and herbivores. More broadly, the possibility that plants share information raises intriguing questions about why organisms that compete with one another might also see fit to network their knowledge.
To begin to understand what is going on it is necessary to begin with a bit of vocabulary about herbivores and carnivores. Herbivore is a term used to describe critters that are vegetarians. More specifically, herbivory is when animals eat plants or plant-like organisms. In contrast to carnivores that are animals that eat meat, and omnivores that eat both plants and meat. Richard Karban, an ecologist at the University of California, Davis, studies how sagebrush communicate. According to Karban (2018), when sagebrush is experimentally clipped it releases volatile cues that undamaged branches on the same plant, on different sagebrush plants, and on some other plant species respond to. These volatile cues cause many changes in neighboring plants and some of these changes make the undamaged neighbors better defended against their herbivores. We currently know little about the nature of these cues. Karban further states that, “Blocking air contact between branches makes responses undetectable, indicating the involvement of airborne cues. Methyl jasmonate has the ability to serve as the signal although it remains unclear if it acts in this capacity in nature. I would like to understand the costs and benefits of releasing volatiles cues and of responding to them. His research examines the multiple consequences of these clues emitting cues. For example, how these clues affect neighboring plants, nearby herbivores, as well as predators and parasites of those herbivores as well as the long term fitness consequences for sagebrush of responding to volatile cues.
Based upon these concepts there are now a popular diets for humans that have been popularized by physicians such as Dr. Steven Gundry whose premise in his book is the concept that some plants have harmful by-products called Lectins. Lectins are a kind of protein that can bind to sugar and are sometimes referred to as antinutrients, since they can reduce the body’s ability to absorb nutrients. These antinutrients are even in foods thought to be “healthfoods” in the past. Lectins are thought to have evolved as a natural defense mechanism by plants, they are essentially a toxin that deters animals from eating the plants. These lectins are lethal to bugs and other predators and, according to Gundry and others harmful to humans. Beans and tomatoes and other “nightshade vegetables” with thick skins high in lectins that may cause dietary difficulties for humans. These Lectins are the basis for the currently popular Gluten-Free and Lectin-Free Diets.
The form of communication plants use for their interactions to fend off the predators is still a mystery. We now know that the idea of plant communication is not bunk, and their secretion of certain toxins and smells, and other warnings are real. As for plants hearing? The jury is still out. While it is likely another type of signal but more research is necessary to facilitate an answer.
All Science Fair Projects (2016). Effect of music on plant growth. Retrieved January 15, 2019.
Andres, C. (2011). Are Trees Talking? Good Nature Travel. Retrieved January 15, 2019.
Cameron, D. (2018). Plants have a taste for classical music, but they especially detest rock ‘n roll. The Epoch Times. Retrieved January 13, 2019.
Gundry, S (2017). The Plant Paradox. New York: Harper Collins.
McGowan, K. (2013). The Secret Language of Plants. Quanta Magazine. Retrieved January 12, 2019.
Newitz, A. (2013). The growing evidence that plants can think and communicate. Gizmodo. iO9 we come from the future. Retrieved January 15, 2019.
Pollen, M. (2013). The intelligent plant. The New Yorker. Retrieved January 13, 2019.
Yong, E. (2019). Plants can hear animals using their flowers. The Atlantic, Science, Retrieved January 12, 2019.