by Kathie Hoyer – August 5, 2020

Like perhaps many of you, I took advantage of the abrupt changes in my schedule this past spring to “go” back to school. One of the courses I took was a fascinating look at plants and what they know. My customers often mention that they talk to their plants, that they’ve given them names, or that they regard their plants as children. (This last endearing quality is admittedly dangerous, as all gardeners would therefore have committed murder by neglect if not intentionally.)

Our tendency to anthropomorphize the inhabitants of our gardens is a way of recognizing their amazing qualities that allow them to flourish in conditions we would find intolerable – imagine the immobility of your feet permanently entangled in dirt while rabbits nibble and deer devour your fingers and birds and squirrels nest in your hair! But examining the attributes of plants in terms of their similarities to us (and our children!) has, until recently, been dumped into the wastebasket of research, labeled pseudo-science and unworthy of further investigation. Perhaps you’ve heard of (or remember?) The Secret Life of Plants, the 70’s book that delved into, among other things, the music preferences of plants, “experiments” that subjected to plants to EEGs and lie-detector tests to prove their reaction to our thoughts and intentions, and the Findhorn neo-Druids that enhanced the growth of vegetables by communicating with their devic spirits. The book was so popular that Science roared up in distaste and directed its energies elsewhere, disparagingly throwing the baby out with the bathwater.

With all this in mind, I felt intrigued and tantalized by the title of this course and accompanying book What a Plant Knows: A Field Guide to the Senses by Dr. Daniel Chamovitz of Tel Aviv University. After all it’s been awhile since the debunking of plant ESP – what do we know now that we didn’t dream of earlier? Quite a lot, in fact. Even if you don’t decide to take his course, I highly recommend the book. Using research examples both historical (Darwin looms big here), current and cutting edge, he runs through our senses: sight, smell, touch, hearing, proprioception (spatial sense) as well as awareness and memory, showing where plants may overlap with us, sometimes leaping beyond and sometimes lagging behind.

Here are a few highlights:
·      We’ve all observed how plants bend toward the light and, in addition, most gardeners understand that in some way plants “know” the changing of the seasons. For sight, consider that plants differentiate between colors – “using blue light to know which direction to bend in and red light to measure the length of the night” which will indicate the changing seasons.
·      After harvesting your tomatoes, I’m sure you’re quick to wash off the musky smell given off by their leaves. For smell, consider the parasitic plant dodder (Cuscuta pentagona) which needs another plant in order to be able to photosynthesize. Research has shown that the dodder can “smell” the tomato plant just as we can and will choose it over a wheat plant.
·      Watching the winding dodder tendril looking for the tomato leaf in that YouTube is also an example of the sense of touch in plants. Chamovitz also uses research done with both the Venus flytrap and mimosa leaves to demonstrate the chemical electric potential of plants in response to touch. On the genetic level, he presents research on the TCH genes which are activated by touch and are ‘turned on,’ triggering a series of reactions that produce calcium-related proteins involved in the action potential at the cellular level.
·      When contemplating hearing in plants, Chamovitz speculates about possible direction of further research but concludes that as sessile beings, rooted in place, plants have not evolved to hear because they can’t flee. But in the online course, he adds in a new section, revising the previous video to present new research showing that some of those TCH genes previously identified as responding to touch, are actually responding to sound waves. In this way, he provides a great example of the premise of the course: that science is continuously evolving and that ideas worthy of research will, eventually, resurface to be explored.
·      At this point we’ll note that taste is not included, and in his book Chamovitz mentions only that taste and smell are ‘intimately connected.’ I suppose no one has yet figured out how to ask a plant if their xylem and phloem are distinguishing between toxins and nutrients, even while we routinely use ‘straw’ and ‘suck’ to explain their form and function and accept that there are mechanisms (preferences?) in the root hairs that absorb water and minerals while rejecting other products in the soil. Somewhere out there, a hypothesis is forming…
·      The sixth sense, proprioception, is observed in the parts of plants that “know” in which direction to grow: the roots grow down, the shoots grow up. Experiments at the beginning of the 19th century using a waterwheel to provide centrifugal force seemed to prove that gravity was in play. Subcellular research of the root caps of plants revealed the mechanism of how they react to gravity, but it wasn’t until experiments were conducted in the weightless conditions of the space shuttle that the necessity of gravitational force to “knowing down” was shown.

Dr. Chamovitz concludes his book (and the course) with examinations of memory, intelligence and awareness in plants which are both fascinating and difficult for me to recapitulate. So I will throw down the challenge: why not explore for yourself? The next rainy day, let your mind wander in a virtual garden and really get to know your plants.

Or, maybe, let them get to “know” you!

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For more information:

Chamovitz, Daniel. What a Plant Knows: A Field Guide to the Senses. New York, Farrar, Straus and Giroux, 2012.

Understanding Plants, Part I: What a Plant Knows is taught by Professor Daniel Chamovitz on Coursera.