In my AP Biology class, we were discussing a peculiar phenomenon in certain plants; when under attack by herbivores, some species seem to be able to signal nearby members of the same species, who then respond by secreting noxious chemicals that repel the attackers. This response has been observed in sagebrush, clover, a species of African acacia, and several others.
One of my students asked how that communication was accomplished. I replied that it was all done by volatile chemical signals -- the attacked plant produces something like an animal pheromone, which then moves via the air to the surrounding plants. The binding of that signal chemical onto receptors in the nearby individuals initiates synthesis of nasty-tasting compounds that discourage the herbivores from chowing down.
"If that chemical could be synthesized," one student asked, "could this be an easy and low-impact way of controlling plant pests?"
"That's a great idea," I said. "It would depend on whether the specific signal chemical has been isolated." And not knowing whether it had been, I started to do a little research.
A quick Google search turned up a number of sites describing reputable, peer-reviewed science (and it turns out that in some cases, they know what the signal is, and in others they appear not to). So far, so good. But then I noticed that about half of the hits I generated suggested a different explanation -- the plants were engaging in mental telepathy.
In fact, one unintentionally hilarious site, Psychobotany, goes into great detail about the possibility of humans telepathically communicating with plants (or vice versa). As evidence that this might be possible, it dredges up the tired old pseudo-experiment by Clive Backster, who in the 1960s attached a polygraph machine to a plant, and threatened to hurt the plant, and the polygraph machine went crazy. (The site conveniently doesn't mention that because of the amazing claims and the simplicity of the experimental design, Backster's experiment has been redone about 10,000 times since he first published, and nobody has ever been able to replicate his results.)
I find it maddening how quickly people want to leap to a supernatural explanation when someone reports something odd. Richard Dawkins calls this the "Argument From Incredulity;" the world is weird, wonderful, amazing, and I don't have a ready explanation for what I'm seeing, therefore it must be __________. Fill in the blank with your favorite paranormal explanation -- ESP, aliens, ghosts, spirits, god, the devil, etc. etc. etc. Scientists are frequently accused of arrogance -- "You think you're so smart, you think you have all the answers." In reality, the opposite is true. If you're not comfortable with being in a state of ignorance, you won't last long in science, because the first thing you discover when you go into science is how little we actually are certain of. This, to me, is one of science's strengths as a model; presented with anomalous data, a good scientist is perfectly willing to suspend judgment, indefinitely if need be. Only a theory that explains all of the available data is good enough, and even then, there's a tentativeness about good science -- a sense of, "well, this is what we think now, but things could change if we get new information." As Albert Einstein once said, "A thousand experiments could never prove me right, but one could prove me wrong."
The supernatural explanations, on the other hand, strike me as cheap cop-outs. If you call plant communication "botanical telepathy" you don't have to go any further; you can sit there and enjoy your little mystical shiver up the spine, and you're all done. There's no need to provide a mechanism, to look for details of how such a thing might be accomplished. You've made your pronouncement about how the world works, and there it ends.
And in contrast with science, which shifts its stance if contrary data is found, supernatural explanations are notorious for clinging on like grim death even in the face of mountains of evidence. The Psychobotany people even cite the study done with pheromonal communication in sagebrush, but oddly, they neglect to mention that the effect went away when the researchers placed plastic bags over the sagebrush plants. This result brilliantly supports the chemical signal hypothesis, but is a little hard to explain if you buy telepathy. Does plastic block Psychic Energy Rays, or something?
Myself, I have no problem with Not Knowing Stuff. This sometimes bothers my students. When I'm asked about things for which science has yet to find evidence, but which can't be ruled out on a theoretical basis -- things like alien visitations, Bigfoot, and life after death -- my answer is, "the jury's still out on that one."
"Well, do you believe in it?" they often ask.
My response is that I neither believe nor disbelieve in anything without sufficient evidence, or at least a strong logical argument one way or the other. In the absence of either -- for instance, in the case of Bigfoot, where there's no particular biological reason that it's impossible, but there's also never been any hard evidence -- I am completely comfortable with adding that to the big old pile of stuff I don't know about.
On the other hand, in the case of the telepathic trees -- I'm pretty confident about that one. "Psychobotany," my ass. I think this time it's Science 1, Woo-woos 0.