Posts Tagged ‘evolution’

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.

*******

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.

*******

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.

*******

Mimosa plant, after

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

Persistence Hunting

August 31st, 2011 | Meera

I have always been stubborn, and I have never been able to run.

As to stubbornness: I have stood my ground, bruised and bloody-minded, so many times over so many things that the specifics blend into each other; a plate of vegetables I refused to eat at age six resides in the same part of my brain as an apology I refused to make at age twenty seven.

As to running: I have tried it so few times with such pitiful results that the specifics are horribly stark; a single night-excursion with A. through the stony streets of Jerusalem, ending mere minutes later in shame and sweat and heart palpitations, is as vivid as if it had been stitched into a medieval tapestry and hung on my wall.

A few years ago, when Ross and I lived in Boston and I volunteered as a gallery guide at the Harvard Museum of Natural History, we used to go there fairly often to listen to public lectures in the evenings. The details of most of the talks we attended—on, for instance, the physiology of singing insects or whether morality is learned or innate—are lost to memory.

But one event in particular impressed me so much that I still think about it from time to time, and it has been on my mind this week. It was by a Harvard researcher named Daniel Lieberman, an anthropologist who studies human evolution. At the time, Lieberman was obsessed with the question of how and why we run.

The conventional wisdom about locomotion, he argued—that early hominids whose bodies were more suited to bipedalism were the ones who survived when they left their shady tree-dwelling lives to forage for food on the open savannah, and that the human ability to run was simply a byproduct of the ability to walk—was all wrong.

Listen, he said: Our cousins the Australopithecines could walk on two legs, and their bodies—hunch-shouldered, short-legged—were nothing like those of the genus Homo. Plus, Australopithecines continued to lead a partially arboreal existence for millions of years, even after they evolved to be bipedal.

Walking, Lieberman announced to the room, didn’t bring us down from the trees, and it didn’t give us our human shape.

Running did.

Only look: The human body is exquisitely well-designed to run. It has long, elastic tendons in its legs and feet that store energy like springs when compressed, something we do much more when we run than when we walk. It has large gluteus maximus muscles that pull our torsos backwards and keep us upright when we lean crazily forward into the off-balance pitch that starts each new step of a run. It is relatively hairless, and can sweat—both adaptations that allow us to release the heat of extreme exertion.

The reason we evolved to lope, dash, scamper, gallop, hurtle across this great green Earth?

Well, the anthropologist grinned, we hadn’t yet invented the bows and arrows that would enable us to kill over long distances; we hadn’t yet tamed the wild horses that would one day carry us close to fleeing animals.

We learned to run, he argued—and run, and run, and run—so we could hunt prey to exhaustion, track it for hours if necessary, past the point at which a quadruped (built to gallop only for short distances) would have to stop to pant. And then we would stop running, too, and have done with it.

I remember being struck, at the time, by how extraordinarily steely this seemed—how the idea of it made me simultaneously marvel at and recoil from my strange, inherited human self. If this was true then we were born to conquer; born to do it without tools, without thought, and without guile, but through a simple act of complete and total obstinacy. To run, it seemed, was to be stubborn.

I have always been stubborn, and I have never been able to run.

For thirty-two years I have lived with both these ideas about myself. But (ask a Harvard anthropologist!) being deeply contradictory truths, perhaps it should not so much surprise that one of them would someday fall.

So far this week, heart and legs and mind stronger than they have ever been from a summer’s worth of field work, I have run a total of nine miles—by the lake, at the gym, through the streets of my neighborhood in Hyde Park. It isn’t much, I know; nine miles is far from an endurance-run across the Kalahari. There is a long, long way to go.

But I have not stopped to pant. I am persisting. I am claiming my strange, inherited human self.

And one of these days I’m going to outlast whatever it is I’m hunting, and have done with it.

lake run

(This is the 3-mile route Ross and I have been running.)

*******

(You can read more about Lieberman’s work in his 2004 paper on the evolution of running, or in any of a number of popular articles it spawned.)


On Tame Sows and Wild Boars

December 30th, 2010 | Meera

When I got to the prep lab this morning, Dave had set out two birds for me to work on: a Savannah sparrow (a species with which I am becoming quite familiar) and a sleek, long-tailed Yellow-billed cuckoo. As the cuckoo thawed, however, it became clear that it had begun to spoil—this happens sometimes when a specimen doesn’t make it to a freezer soon enough after its death—and that it wouldn’t, therefore, make a good study skin. Birds whose tissues are breaking down have skin that falls apart easily, and they inevitably lose a great deal of feathers as you go along. So Dave put the cuckoo back in the freezer to become a skeleton on another day, and drew out as a replacement an exquisitely tiny Golden-winged warbler (Vermivora chrysoptera). As I’ve gotten more comfortable working on small birds, Dave has given me a good many warblers to prepare—but this Golden-winged was the first of its kind that I had ever seen. While he was taking it out of the freezer, he also told me that they aren’t a very common find around here—and so I hoped I would do a good job with the perfect little creature he placed by my tray.

Fortunately, she was kind to me, and turned out beautifully. (I can use the pronoun with confidence because later I placed a pair of magnifying goggles over my head and personally examined the minuscule, very slightly raised, very slightly shinier spot behind her kidneys that Dave, with fantastic authority, indicated as her ovary. To me it looked like a microscopic, colorless oil slick sitting on top of a larger, vaguely less lustrous oil slick. Sexing birds when it isn’t mating season is an exercise in seeing what does not want to be seen.)

But besides being beautiful (Golden-winged warblers have, as their name suggests, bright yellow plumage on their wings—but they also have golden crowns, striking patches of jet black on their faces and throats, and the most modish gray feathers you can imagine cloaking their backs), it turned out that the bird I met today was also a player in a long and fascinating history.

364

Here’s how it goes. The first thing you ought to know is that the Golden-winged warbler happens to have a kind of aural twin. One of the main songs you’re apt to hear these birds sing is a two or three-note whistle that is usually described as a high, gentle buzzing, like someone breathing in and out over the surface of a nail file. But hearing that song isn’t always enough to make a positive identification, because another warbler—the much more common Blue-winged—buzzes in a very similar way. And it’s especially apt to do so if it has a little Golden-winged blood in it.

Here’s why it might. The two species of warbler don’t look all that much alike; although they share the same basic colors, the way those colors are distributed on their bodies is quite different. But DNA tests reveal that they’re incredibly similar genetically. In fact, scientists believe that two or three million years ago, Blue-winged and Golden-winged warblers were one and the same. At some point, though, glacier movements across North America caused the population to split into two groups: one isolated somewhere around Missouri, and the other somewhere up in the Appalachians. And from this separation came speciation.

For more than a million years, Golden-winged warblers and Blue-winged warblers were kept apart from each other mostly by dense forests, a habitat in which neither is able to thrive. Eventually, however, humans began clearing those forests and farming them—then abandoning that farmland and allowing a sparser collection of trees and shrubs to grow back. As this change in the landscape occurred, sometime between one and two centuries ago, Golden-winged warblers began moving north and Blue-winged warblers south. And because they still share so much genetic material, when the two meet, they are happy to breed with each other.

If a Golden-winged warbler mates with a Blue-winged, the two produce a reliably identifiable hybrid offspring known as a Brewster’s warbler. (A Brewster’s warbler is then able to mate with either a Golden-winged or a Blue-winged warbler in a process known as a backcross; these pairings, and their successive pairings, produce all manner of other subtly different and unpredictably plumaged birds, as well as—occasionally—another reliably identifiable hybrid known as a Lawrence’s warbler.)

Unfortunately, besides making for an incredibly complicated family tree, this habit of hybridization has spelled a precipitous decline in the Golden-winged warbler population. That’s because Golden-winged warblers are significantly more likely to mate outside their species than Blue-winged warblers, and—much to the chagrin of avian anti-classists, I presume—once they’ve done so, their hybrid offspring aren’t able to find mates as easily as pure-blooded birds. The combination of these two things has meant that, as the species have crossed paths over the past century or so, Blue-winged warblers are making pretty good headway at displacing Golden-winged warblers.

What truly amazes me about all this, beyond the fact that it’s biologically fascinating, is that I know perfectly well the whole story was present in Dave’s head as he handed me that sweet little specimen this morning—even though the only thing he said was “We don’t get too many of these.” Sometimes I wonder what it can possibly be like to know as much as he does about birds; how it must feel to have all this detail stored away inside him as comfortably and naturally as, for instance, you or I might store our feelings about our best friends.

You may have heard, if you live in Chicago and happen to be a newshound, that Dave’s retiring from the Field after 35 years of service. He’ll still be there every day for the next year, but when he does eventually leave it will be a loss beyond words to the division. I can’t tell you how lucky I feel to have spent the past two years working in his lab. And do you know what? If I were that Golden-winged warbler, I’d feel lucky to have passed through it too.

P.S. I owe a debt to Todd McLeish’s excellent Golden Wings & Hairy Toes: Encounters with New England’s Most Imperiled Wildlife.

P.P.S. Anyone curious about the title of this post might want to take a quick look here.

On the Persistence of Ferns

July 7th, 2009 | Meera

On an early January day in Chicago this year, my muscles twitching in protest of the cold and the sky around me bright with winter sunshine glancing like arrows off the curves of strangers’ sunglasses, I stepped into the Fern Room of the Lincoln Park Conservatory to warm my face with the humid breath of the forest primeval.

If you have never had the pleasure of visiting the Fern Room, the best way I can think of to describe it is to tell you that it is a place where all the colors of the spectrum seem to have been suddenly replaced by a hundred thousand different shades of green. The light that outside was so harsh and dazzling is now filtered through shady fronds of emerald, jade, and olive, and instead of walls and corridors the stout trunks of cycads and the lacy leaflets of ancient ferns divide the room into secret passages and broad arcades. At every turn you begin to expect a horned triceratops or armored ankylosaurus to push through the vegetation, shaking its head and crying, What—is it you? For shame, for shame! You’re sixty million years early!

I came for the cycads, having just read of the endlessly charming Oliver Sacks’ journey to a remote Pacific Island in order to run his hands along their stiff, glossy, blade-like leaves, beguiling but toxic suspects in his search for the source of a strange disease of the mind. But it was the ferns that captured me. I liked their delicately forked fronds, each one divided into innumerable leaflets, called pinnae, that spread outwards like gentle fingers touching the air. Some curled this way and that, and when they did I could see that they were studded with neat lines of rough buttons on the underside. The buttons were called sori, I learned later, and each little nub of a sora held clusters of sporangia, themselves tiny round bubbles holding even tinier spores—these last, as fine as dust, the powder of the next generation.

growth

In the time of Shakespeare, people didn’t know about spores. They thought it obvious that ferns, like all other sensible plants, propagated themselves through seeds, which are eminently practical devices that contain not only the embryonic beginnings of a new plant, but food for the road as well, and have smooth, smart coats to protect them from the elements. (Spores, which are single-celled motes almost too small to see, seem impoverished by comparison.)

But since, five hundred years ago, not a soul had yet recognized the brown patches on the undersides of fern leaves as containing reproductive particles, it began to be believed that the so-called seeds of ferns were cryptic, secret things, not simply well hidden but, in fact, invisible. And like spores that fly far from the fronds where they were first exhaled, that idea traveled and grew. Eventually, wondering herbalists transformed it into the astonishing claim that if you could, somehow, collect the elusive fern seed (say at the moody hour of midnight on Midsummer Night’s Eve) and clutch it in your hand, you yourself would be veiled from the prying eyes of others. In the words of a thief from Henry IV, about to embark on an ambitious robbery, we steal as in a castle, cock-sure; we have the receipt of fern seed—we walk invisible.

It is a very pretty notion indeed, but if I were to steal an essential quality from a fern it would not be invisibility, but persistence.

It isn’t easy to contemplate the earth in its wildest, most wonderful days of youth, but when we do picture it, ferns are the plants we see in our mind’s eyes, blanketing the new world in a riot of green fronds and settling their wispy roots into a rich black soil. The very oldest of ferns are almost impossibly ancient, at least from the perspective of complex living things, some 345 million years old; that makes them older than the dinosaurs, older than flowering plants, and far older than any fuzzy bee that they might otherwise have relied upon to pollinate them. They were giants, then, too, snaking up to the height of ten-story buildings. After the dinosaurs dwindled and died, and almost every other form of life went with them, ferns returned first of all to make the earth verdant again. They grew close together, like brothers, and shielded the soil, and gave other green things the time they needed to revive.

Not only old, ferns, not only huge, not only tenacious, but also numerous: their tally during the Carboniferous period, when they first appeared, was so great that when they died, their remains helped to form vast coal beds all across the earth, hundreds of miles wide and hundreds of feet deep. For hundreds of years we have mined the bodies of ferns to fuel our industry, build our cities, and sustain the needs and desires of our daily lives, and still we have not managed to exhaust their reserves.

What is perhaps even more astonishing is that throughout all these long eons, many ferns have continued to unfurl, generation after generation, into the very same forms they have always had, altering very little about their strange, self-sufficient design. Soft brushes wielded by eager paleontologists, for instance, have gently pushed the dirt from two hundred million year-old fossils of Osmunda clatoniana. Today, the same fern continues to put forth its long, fuzzy stalks in rich woods from Newfoundland to Manitoba, South Carolina to Arkansas, and every point in between.

Its common name may be the “Interrupted Fern,” because tiny brown leaflets, fertile with hundreds of thousands of spores, break up the smooth green lines of its fronds—but its lengthy existence on this earth has been anything but. The same answers that made sense to it two hundred million years ago still make sense now: it has the same leaflet shapes, the same reproductive mechanisms, the same root systems, the same way of throwing up a circlet of fronds from a single central spike, as if fashioning a fringed fan with which to stir the air around an ancient deity.

"A small dinosaur would feel at home...

Consider the stubbornness, the sheer dogged tenacity, of those two hundred million years, against these other figures: the species lifespan of the average flowering plant is only about 3.5 million years—a blip of a figure that closely parallels the species lifespan of the average mammal. Having reached that ineluctable expiry date, most living things give up the ghost, hand over their space on the planet to some newer, upstart species better suited to the planet’s changing circumstances.

Consider this: our own species, even with all our long history of literature and progress and scientific endeavor, and despite the fact that we have been around long enough to dream delightful dreams about fern spores and invisibility and awaken to learn that they are false, still, Homo sapiens has only had a mere five hundred thousand years, give or take a couple of hundred thousand, to work on its routine.

Two hundred million years, and how much more than we has the Interrupted Fern already seen? How much will it witness, after we are gone? How it must yawn, to look upon the petty wars and conquests of human affairs. How wise it is to stay so long the same.

I am not like the ferns. I have spent my thirty years on changes and modifications, constantly refashioning my own shapes, mechanisms, and systems in the hope that there is, after all, a better answer. I have been shy as often as I have been bold; I have worn the crown of ambition as often as the mask of nonchalance; I have copied friends and enemies, believing their shapes an improvement over my own. I have been myself a dozen different ways, and still never found the right one. I am trying out a new incarnation right now, in fact—fingers crossed that this time I know what I’m doing—if only you could see me shift.

I admit that I am tired from all this transmuting. I long for those two hundred million, long to stretch like that. Long to peer out beyond the glow of my own small candle flame and gaze at all that has come before and all that will come after. I am hungry for the peace that I imagine must accompany such a lingering existence.

human contact

And yet, you know, the funny thing about it all is that when your thumb is as inky-black as mine, the lives of plants seem fleeting and fragile.

I once killed a succulent, those hardy green survivors that—like camels—hoard water within their fleshy parts for dry days, by deciding that the most logical place for it was atop a radiator in December. There it baked and shriveled and, inside two weeks, limply relinquished its grip on life. Growing things beyond number have expired under my care, littering my past with inglorious remains: basil; rosemary; cilantro; narcissus; aloevera; bamboo. Just this afternoon I was re-potting six tiny transplants, baby tomatoes and strawberries grown from seed by a friend with more verdant talents—and even as I gazed upon them tenderly, a faint, funereal voice seemed to whistle past my ears: Poor things, it sang. They’ll be gone before the summer’s out. Every pot on my back deck is a memento mori, a reminder of the impermanence of all things.

But there are different measures of longevity. By one, the meandering lifetime of a human gardener, seventy or eighty years long, stretches out like an eternity, punctuated by the small gasps of scores of individual plants that unfurl and pass away within a season in yard after yard, home after home. By another, the entire collective lifetime of the human species is but a gasp itself—at least when compared with the persistence of ferns.