Archive for December, 2011

Lessons from Plants in Pain, or What We Talk About When We Talk to Ourselves

December 14th, 2011 | Meera

Roald Dahl, sovereign of the strange idea played out in matter-of-fact sentences, once wrote a story about a man named Klausner who invents a sound machine. With it he’s able to hear rarefied notes—tremors of the air that otherwise range, like so many things, outside the limits of human perception. When he turns on his invention, Klausner finds himself initiated into an entire universe he hadn’t known existed: a universe of plant communication.

You might think, on the face of it, that this would be a fine and lovely thing. You might think of how you generally experience the green and the growing, and imagine Klausner entering a soundscape filled with music, strains that match the beauty of a field of wildflowers or the elegance of autumn leaves. But instead, he mostly apprehends the noises of plants in distress. “Fierce grinding discords” fall on his ears: he’s shocked by the shrieks that roses make when they’re clipped off the bush. He’s tormented by pity when he hears the awful moans of a tree trunk split by his own axe.

Dahl leaves the question of whether the machine really works open to interpretation—but what I like about the story doesn’t rest on the definition of Klausner as either brilliant or insane. The thing that’s stayed with me, long years after I first read The Sound Machine, is Dahl’s bleak view of what speaks loudest in this world, what he thinks drives the “speech” of all living things—and that is pain.

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343 (Mimosa plant, before)

Most disasters, even if they’re built on long and quiet years of brewing, eventually befall us with what feels like too little warning. A stroke slams down upon the pathway blood must take to brain, a guillotine that splits a thought in two. Your partner’s eyes, warm as summer lakes, freeze over for no reason you can fathom. A midnight switchblade sticks its cutting edge between your ribs; you gasp awake, pinned by the sharp awareness that you’re inside the wrong life. Tomorrow you might lose your job, your home. Be diagnosed with cancer. Even if you know the air is humid with the vapors of oncoming injuries, each one remains invisible until the day it’s churned into a storm.

I don’t think we’d be better off if we could see the future. I’m pretty sure I, anyway, would be flattened by the weight of full omniscience. But some small bit of notice, a clear advisory or two—watch out, here’s danger on the way!—now that, I’d take. Wouldn’t you? I think that wish must have something to do with why so many of us sit ourselves down to write quite undeliverable letters to the people we once were—an act that’s whimsical and sweet, and yet somehow forlorn.

Maybe it’s also why I’ve come to be, especially of late, a great collector of stories about other people’s hurts. (A cheerful philately.) If you’ve been wounded, come and bend my ear. I want to hear your warnings. And sometimes I eavesdrop on damages that strangers speak of. Years ago I spent almost half an hour lingering over my coffee—which was bad—because the girl at the table next to mine, fresh off her honeymoon, was wiping hot tears from her face and telling her companion how miserable she was to be married. She wasn’t my friend. It wasn’t my problem. And I’m not at all proud to have been riveted. But it was impossible not to be. My body rang (unobtrusively, I hope) with borrowed sorrow, and I still recall her cadences.

I think that moment meant so much to me because, respectfully, Tolstoy was not entirely correct about unhappiness. Life doesn’t feel the need to plan new slights and sicknesses to suit each one of us. Its threats recycle. I’m a realist: I know that, private though they feel, my troubles hover at the average, coinciding with those of my species. Whatever has battered some other Homo sapiens may soon come for me, and I would like to start preparing my defenses.

If this sounds ghoulish to you, well. I understand. But you should know that I am not alone in paying close attention to the suffering of my peers for my own sake. I stand with graceful trees: with willows, alders, poplars, sugar maples. The sweetest and most useful crops, as well—pea pods, beans, tomatoes, cotton—are selfish just like me. And ears of barley, ears of corn—these listen, too, to their beleaguered neighbors.

Klausner (tender soul!) was driven nearly mad by sadness when he overheard plant pain. He called a doctor for his broken tree and made him paint iodine in the wound. Plants themselves know better what to do.

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It was in the early 1980s that a few scientists first began to report on trees that seemed to send each other stress signals. One was a zoologist named David Rhoades, at the time studying Red alder (Alnus rubra) and Sitka willow (Salix sitchensis) defense mechanisms at the University of Washington. Rhoades fed caterpillars leaves from trees their brethren had previously attacked. He found that they began to lose their appetites, and often died prematurely. Presumably this was because of some chemical compound the trees were able to release into their leaves as a form of rapid resistance—precisely the kind of thing he’d been looking for.

But Rhoades was surprised to discover that the very same thing happened to caterpillars fed the leaves of undamaged control trees, planted a little distance away. Could the attacked trees be emitting some kind of pheromonal warning that their counterparts could “hear?” Could they be telling their fellows to put up a fight against their leggy foes?

This study inspired a similar experiment on potted poplars (Populus euroamericana) and sugar maples (Acer saccharum) by a pair of researchers at Dartmouth. Jack Schultz and Ian Baldwin found higher concentrations of mildly toxic compounds called phenols in trees whose leaves they had torn. They saw the same thing when they checked on unscathed trees, after they were exposed to air pumped in from the chamber where the damaged trees were housed.

The scientific community as a whole reacted to these findings with great skepticism, some of which was not undeserved: methodological problems and an over-confident interpretation of statistics tainted both sets of results. But there was also, apparently, not a little ridicule, with some ecologists scoffing over the idea of “talking trees” and animal behaviorists closing ranks around the definition of communication.

In hindsight, this part of the negative response was somewhat less justified. In the first fourteen years that followed Rhoades, Schultz, and Baldwin’s reports, only three studies regarding plant-plant communication were published (perhaps because of the disbelieving atmosphere they would have emerged into). But times have changed. According to this overview of the literature on the subject, that figure increased to nearly 50 papers between 2005 and 2010.

At this point, the evidence that plants can receive, act on, and benefit from specific signals produced by their distressed coequals is pretty compelling. We’ve learned, for instance, that corn seedlings primed with compounds released by damaged plants give off more of their own defense hormones and chemicals when subsequently slashed with a razor blade or painted with caterpillar regurgitant. (Science is cruel.) We’ve learned that certain unrelated species, like sagebrush and tobacco, can interpret each other’s cues about dangers like hungry herbivores or clipper-happy researchers. We’ve even learned that well-watered pea plants, having overheard a warning from a thirsty neighbor, can pass on that message to still other plants, further away—although this game of vegetable Telephone seems to be played through the medium of soil, not air.

In my favorite recent study, which delights me more because of how the plants defend themselves than how they talk about it, Lima beans infested with spider mites—as well as those exposed to leaves from infested plants—react by activating a set of genes that trigger the emission of a volatile organic compound. This compound, in turn, attracts spider mite predators that come and hoover up the pests.

How wonderful is that? I call it very wonderful, especially since our own apartment has witnessed the expiration of a beloved dwarf Meyer lemon tree that succumbed to a spider mite blitzkrieg. If we’d had two trees, I wonder if one could have saved the other?

Maybe what Dahl got wrong was not the thought that pain is the seabed of all our most essential speech. Maybe where he erred was in suggesting that the anguish Klausner heard was simply that: anguish, pure expression with no purpose and no useful end.

I think of myself sitting at a coffee table, leaning in, despite my better judgment, and breathing in the chemistry of someone else’s heartache. In my mind, now, I see it as a moment of anointment, an inoculation. I think this even though I have no way of measuring what changed in me because of it.

Our bodies fail. Our partners leave. We wake up sick, or shipwrecked. Shocked. And I am hungry to be put on guard, to know when something wicked this way comes.

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It’s clear that unscathed plants do eavesdrop, like me, on strangers in distress, and make themselves stronger when they hear of trouble. What’s less clear is what is happening for the plant in pain. Is its anguished warning—Watch out, danger!—really meant to serve as counsel to the ones around it? It’s possible, of course, that some plants evolved to give off stress signals altruistically, because neighbors are often kin, and one example keeps the group as a whole safe. But many times, letting a neighbor in on danger makes you more vulnerable. A Lima bean plagued with spider mites might not want its compatriots to be protected by mite-eaters. (One lemon tree might have saved another, but reluctantly.)

Instead of selfless exhortations, the story of plant stress signals seems at once more simple and more strange. The thing is, a plant that’s hurt and sending out a warning is very likely talking to itself.

Most plants have sophisticated vascular systems, and that’s often how they transmit chemical messages. But volatile compounds, diffusing through air, can travel faster than molecules moving against gravity through tiny tubes. Airborne signals also allow parts of a plant that don’t have a direct connection to each other to speak. Why, though, would a plant need to warn itself? What does that even mean? Well, think of this: A caterpillar munching on one leaf will probably move on to another, a little ways off. That second leaf has time—not much, it’s true, but some small span—to put up its own garrison against the tyranny of tearing insects. That second leaf is far from doomed. And it could use some notice. A body needs to take care of itself.

Most disasters befall us with what feels like too little warning. But maybe that’s because, wrapped up in where we hurt right now, we don’t imagine taking steps to care for what is still undamaged. I know; we are not plants, with separate fates for separate parts. When I’m in pain, it feels as if I ache completely, my entire consciousness consumed by one calamity. And yet. Could there be, do you think, something in this selfish signaling? Some way for us to be like willows and like alders?

I’m not entirely sure. But this past year, and nearly two, has felt like injury to me; so now seems like the time to test the case. I’d rather not be Klausner’s roses, crying out futility. I’ll trust instead that there is strong and healthy matter that remains in me, and let the weaker parts speak loudly to them. More importantly, I’ll try to listen and to learn. Because it’s not, I think, too late to start talking to myself.

And you? Ah. If you eavesdrop, let it be.

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Mimosa plant, after

Highly recommended further reading: This wonderful article about visionary biologist Chandra Bose, and his experiments in plant sensation and behavior.