A walking, sentient plant has been the inspiration for writers since the early-mid 20th century including the Ents in J.R.R. Tolkien’s The Lord of the Rings, the Triffids in John Wyndham’s Day of the Triffids, and Audrey II from Little Shop of Horrors. Folklore and fairy stories have mentioned trees talking and moving around as a way to make people lose their way (and I would think possibly their minds) in the forest. Maybe this is not so far from the truth; the talking that is, not the walking part.
Ever since I was a child, I was fascinated by the prospect of communicating with animals and plants and thought that it was only a matter of time before this could be proven to be true. The animal part of this thought has met with moderate success in a number of interactions including Koko the gorilla and Kanzi the Bonobo among others. But what could we learn from a 300 year old tree if there was a way to “speak” to it? Putting aside the likelihood of humans communicating with them, do plants communicate with each other? It is a fascinating premise; trees that communicate and have a sense of self but more research is being done to figure out just what is going on in the “mind” of a plant.
As 
strange as this may seem, there have been studies done in this field. Charles Darwin, with his son Francis, had much of his career as a biologist dominated by the study of botany. One of the last books he had published was entitled The Power of Movements in Plants. Leading botanists at the time dismissed their ideas and claimed their work was nullified because they were amateurs who performed careless experiments and obtained misleading results. The Darwins found that plant actually had much more movement than once thought, although at a slower rate than their animal counterparts. Plants move depending on the time of day, the position of their light source, their access to water, etc. More than 200 years later, many of their ideas are getting some interest again (at least, indirectly). Recent advances in have been made in plant molecular biology, cellular biology, and electrophysiology revealed that plants are sensory and communicative beings.
Researchers have found that plants are not the passive entities they were once thought to be. (I am still hoping to see a wandering hemlock tree deep in thought when I am hiking in Algonquin Park.) Plants may be most definitely rooted to the spot where they sprouted but they are also capable of communication. Plants communicate through the air with the release of volatile organic chemicals (VOCs), throughout the soil by secreting chemicals, and studies have even been done concerning the sounds that plants make to other plants and insects (these last studies have been met with degrees of acceptance from the scientific community at large). Let us take a closer look at some of these communications.
Distress signal. When a plant is attacked by any invader, it can send out a chemical distress signal. As an example, when a wild tobacco plant is attacked by a hornworm caterpillar, the plant can identify it by its saliva and send out a chemical signal called green leaf volatiles that appeals to this caterpillar’s enemy, the big-eyed bug (yes, that is actually its name). Within hours this enemy will show up to eat the caterpillar thus saving the plant from being completely consumed by the ravaging caterpillar. That smell of fresh mown grass is another example of an SOS signal.
This SOS can be picked up by the surrounding plant life – even different species – which in turn ramp up their defenses against the invaders with their own chemical warfare. This is a preemptive strike to help defend it while its neighbour is being attacked.
Plants defend their territory and their sprout-mates. Plants have to compete for food, water, and sunlight like almost every other living thing out there and are capable of pushing out their competition. The invasiv
e spotted knapweed has a root system that releases a chemical called (-)-catechin into the soil that is toxic to the native plants it displaces. It immediately destroys the roots of other plants thus guaranteeing its proliferation. Lupins have formed a defense against this European invader with their secretion of oxalic acid which acts as a barrier against the toxins released by the knapweed and can even help to protect other species. The knapweed is not alone in its chemical warfare. Other species of plants also have this ability to taint the ground around them including cedar and sunflowers.
Plants recognize their own and are more considerate of their own kin. An experiment using Great Lakes sea rocket illustrated this theory. The researchers planted four plants into each pot – either all related or all unrelated – allowed them to grow for a period of 8 weeks until they started to bloom. At this point they uprooted them to see how the plant, stem, leaves and roots had developed. The related plants were much less inclined to encroach upon their neighbour’s space than they were with unrelated plants. How much of this cooperation would be witnessed in times of scarce resources is yet to be seen.
Plants can communicate with animals. Scientists have discovered a carnivorous pitcher plant in Borneo that has developed a way to entice bats to roost in it so that the plant might benefit from the bat’s excrement. The plant has a strong echo reflector that bounces back to the bat so it can find the plant. This is a mutually beneficial relationship; the pitchers provide a comfy spot to roost with few parasites and the bats poop in the plants which provides the nitrogen the pitchers need.
Sound and electricity. Studies are currently being done in these two areas. In the 1960’s it was discovered that declining health of a plant can be detected by listening to it. Bubbles within the plants caused by respiration during photosynthesis are detectable and possibly used by insects in their search for a food source. It may be that plants emit and use sound to communicate with each other as well. Australian plant physiologist, Monica Gagliano has been studying this possibility. “We have identified that plants respond to sound and they make their own sounds,” Gagliano said. “The obvious purpose of sound might be for communicating with others.”
Researchers have been studying the electrical fields surrounding plants. Flowers were already known to use bright colours, and enticing scents to attract their pollinators but electricity may also help bees and other pollinators find their way to them.
This evidence should show people that plants may not have the same brain and thinking processes that animals have but they do have systems of communication that seems to have worked for them for millennia. You may not hear a couple of sunflowers sitting around and gossiping about the neighbouring coneflower but plants are “talking” and deserve a little more respect than they have been given up until this point. Show those plants some love and speak to them. They may just have something to say.
–Janice Willson
A short TedTalks about this subject:
https://www.ted.com/talks/stefano_mancuso_the_roots_of_plant_intelligence
A couple of articles on this topic if you are interested:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2634023/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2819436/
