by Oliver Sacks
Boone’s Spanish seems as fluent and idiomatic as that of the local Oaxacans—he is earnestly conversing now with Fernando, the driver’s son. Fernando is perhaps sixty years Boone’s junior, but they are completely at ease with one another, the old man and the boy. Indeed, I get the sense that he is seen as something of a father figure by the local people.
I remember now—I failed to make the connection earlier—that Mickel and Beitel’s book, the fern bible, is dedicated to Boone, for it was Boone who originally suggested to John that he catalog the ferns of Oaxaca. Oaxaca, he said, was probably richer in ferns than any other state in Mexico, and also among the least studied. Incited by Boone’s suggestion, John had made a series of trips during the sixties and seventies, collecting nearly five thousand specimens from all over the state. Boone himself contributed another five hundred in the early seventies, many of them rarities. By 1988, when the Flora was published, John and his colleagues had discovered no fewer than sixty-five new species of fern, and catalogued a grand total of 690 species, in Oaxaca alone. Boone had been behind all this, providing room and board, guide service, logistical support and transportation.
Here in Mexico, Boone is saying, you have to use your brains to know what’s going on. In the States everything is published, organized, known. Here it is under the surface, the mind is challenged all the while.
The richness of Oaxaca’s ferns seems miraculous, for there are no more than a hundred or so in New England, perhaps four hundred species in the whole of North America. There are ferns in all latitudes—a brave thirty species in Greenland, for example—but far more as one goes toward the Equator. There are nearly 1,200 in Costa Rica, where Robbin teaches a course every year. And there is an incredible variety of shapes, sizes, formats, whole families of ferns with no exemplars in the temperate zones. In Oaxaca, too, there is every sort of habitat, from the arid central valley (itself a 5,000-foot-high plateau) to rain forest and cloud forest, to mountainsides. Tree ferns, climbing ferns, filmy ferns, shoestring ferns, they are all here, in unparalleled diversity.
Robbin’s mind and mine, we discover, have both been going back to the little hornwort we had seen near the stream, with its precious, symbiotic freight of nitrogen-fixing bacteria. We are bathed in nitrogen, the atmosphere is four-fifths nitrogen. All of us, animals and plants and fungi alike, need it to manufacture nucleic and amino acids and peptides and proteins. But no organism other than bacteria can make use of it directly, so we are all dependent on these nitrogen-fixing bacteria to convert atmospheric nitrogen into forms of nitrogen the rest of us can use. Without this, life on Earth would not have got very far.
Intensive cultivation of a single crop tends to deplete the nitrogen in the soil quickly, but the Mesoamericans discovered early on, as other agricultural people did, by trial and error and experimentation, that beans or peas grown along with the corn could help replenish the soil more rapidly. (It was also discovered that alder trees, though not legumes, could similarly fertilize and enrich the soil, making possible a more intensive cultivation of other crops. The planting of alders had become an integral part of Mexican agriculture by 300 B.C.) In Europe, Robbin points out, many other legumes such as clover and alfalfa and lupin were grown as animal forage, and these were even more effective in restoring nitrogen to the soil than peas or beans. In China and Vietnam, he continues, warming to his theme, the great restorer is not a legume, not a flowering plant at all, but a tiny water fern, Azolla, which engulfs and lives with a nitrogen-fixing cyanobacterium, Anabaena azollae. Rice, half-submerged in rice paddies, grows much more vigorously if Azolla is ground into the mud—in Vietnam, they call this green manure.
Even though this practical knowledge had been around since the Stone Age, no one really knew why it worked, just that it did. Only in the nineteenth century was it realized that the strange nodules often present on the roots of legumes were full of bacteria, and that these, with their special enzymes, could fix atmospheric nitrogen and make it available to the plant (similarly with the nodules on alders, and the Anabaena in Azolla). With the eventual decomposition of such plants, the now-assimilable nitrogen compounds would be released into the soil.*
It was also realized around this time that however carefully one fertilized the soil with compost or with animal waste, however much one grew beans and vetches and clover and lupin, one could not feed an exploding human population without additional, inorganic fertilizers which were extremely nitrogen-rich. By the end of the nineteenth century, it was becoming clear that a nitrogen crisis was pending, that one had to have more ammonia or nitrates available if an exponentially expanding human population was not to starve—the catastrophe Malthus had dreamt of a century earlier. There was a rush on the South American beds of nitrates and guano (the Peruvians had long used these to guarantee a fertile soil), but these were exhausted in a few decades. Thus the supreme challenge, by the beginning of the twentieth century, was to make synthetic ammonia, for there was no longer enough natural fertilizer on the planet.
Now, of course, Robbin shrugs, the world is awash in synthetic fertilizers, and thousands of surplus tons of them drain into our lakes, rivers, and seas, disturbing the planet’s nitrogen cycle and causing huge overgrowths of algae and whatnot. Not that this is any help, he adds, to a place like Oaxaca, which is much too poor to afford synthetic fertilizers anyhow. And this was where Boone came in—Boone, who saw, very clearly, from the first, that the farmers needed to be more productive, while remaining autonomous and independent of fertilizers from the U.S., and who wondered whether it might not be possible, by grafting or hybridization, to endow the cereals themselves with nitrogen-fixing bacteria.
Boone himself had found a very tall corn near the town of Totontepec, a corn whose roots had a slimy covering, and, examining this mucilage, he discovered that it contained several sorts of nitrogen-fixing bacteria. He had wondered whether it might be possible to get these bacteria into the corn itself, to breed, in effect, a nitrogen-fixing corn, and has been encouraging others to explore this. With genetic engineering, Robbin added, it might even be possible to bypass the bacteria and insert the gene for the nitrogen-fixing enzyme into the plants themselves.
Back in the bus, we are approaching El Cerezal (“the cherry orchard”), a little village, with no cherry trees that I can see, but pear trees blooming on the side of the road. We have to slow down, almost to a standstill, because of speed bumps (these are called “sleeping policemen”) in the road. They were put here a few years ago, after a village girl was killed by a speeding bus. A hawk flying ahead of us, cries of excitement as it veers to one side of the bus.
I hear someone mutter, speaking of a certain group of ferns: “They’re all pinnatifid.” There is a huge amount of knowledge on this bus. It would be an irreparable loss to systematic botany, I think, if we crashed (as could easily happen, sliding into one of the sharp, precipitous ravines at every hairpin bend of the road).
Misted views of Ixtlán and Guelatao across the valley. Guelatao, Luis tells us, “is where Benito Juárez was born in 1806, the 21st of March. This is a holiday in Mexico.” His life, his upbringing, his mission, is detailed by Luis. “He learned to read with the priests; went to the seminary; met there with philosophers; he took from there some of the ideas and maxims he used in his presidency. Then he went to the University of Oaxaca to become a lawyer. Became the governor of Oaxaca—and finally the president of Mexico, in 1856.” We are treated to an elaborate discourse on the situation and politics of Mexico in 1856. A polite and finally stupefied silence greets this. Meanwhile, all sorts of wonderful plants slide past us.
Church property annexed by the government, its taxes went to the State, its controls and powers also. This reform led to the French invasion. Luis’s voice continues as a background, while I gaze through the window at the village of San Miguel del Río across the valley. Huge bald cypresses, Taxodium, edge the river there.
We are descending now, from a high ridge, into the valley of the Rí
o Grande. “If I can interrupt,” says Boone, getting to his feet (no one else would have had the temerity to interrupt Luis’s dissertation on Mexican history), “We would now be crossing this old steel bridge, which was built in 1898 by the Cleveland Corporation, but sadly, last year, it was destroyed by a dump truck.” The bridge, one end demolished, lies obliquely, half-submerged in the water. J.D., more attuned to birds than the destruction of old things, spots a gray silken flycatcher on one of its posts.
Extraordinary that a man, a Zapotec, from a small village, Luis continues, could become the president of Mexico. With his humble origins, his feeling for poor people, his liberal ideas, he was the Abraham Lincoln of Mexico. Luis goes on to tell us stories, myths, of Benito Juárez’s childhood, little stories which showed his character, pointed to his future greatness and destiny.
Now the bus has climbed again, almost two thousand feet, and we can see the village of Ixtlán uphill to the right. Boone points to his home and botanical station high on a cloud-capped ridge overlooking Guelatao. For about a mile now, he says, there is a new dominant Civocarpus, something macrophylla. (What is a Civocarpus, I wonder?)* He knows every turn and twist of the road, every square mile, of this wild and beautiful country.
I wonder what his story is, what motivated him to come here, as a young man, in the 1940’s.
I get talking with Scott about our primordial need to identify, to categorize, to organize. He himself, he says, rather than spotting species, immediately goes to a wider category—the family—and then homes in to genus and species. How much, we wonder, is such categorizing hardwired in the brain? How much learned? Is “animate/inanimate,” for example, a hardwired category? Or the reaction of primates to snakes? Must baby bats and baby birds be taught their pollination targets? We speak of bird-song, half-wired, half-learned.
Finally we arrive at the Llano de las Flores. John Mickel moves about swiftly, identifying all the ferns: shield ferns, holly ferns, lady ferns, fragile ferns, bracken, sometimes fifteen feet high—all common in temperate regions. And Plecosorus speciosissimus and Plagiogyria pectinata. I love these rolling, Latinate names, redolent of a long-past scholastic age. Clubmosses, lilliputian plants out of fairyland with tiny leaves and cones, clothe the sides of the ravine. There are also many epiphytes, wreathing the trunks of trees, leaving scarcely an inch uncovered. Usually these epiphytes are harmless, clinging to the bark of trees without parasitizing or hurting them—unless the sheer weight of the epiphytes brings the tree down. (I have heard of this happening in the Australian rain forest, where staghorn ferns may weigh a monstrous five hundred pounds or more.)
J.D., off in the bracken, is in ornithological ecstasy, his bulky bearded figure jerks this way and that, as he spots new species, new varieties. Exclamations of delight burst continually from his lips. “My God! My God! Look at that … so beautiful …” His enthusiasm, his lyricism, never wanes, his sense of the birds’ beauty and freshness. He is like Adam in the garden of Eden.
I am fond of bracken, or brake, I confess, partly because the old names excite me. There are fourteenth-century manuscripts that speak of “braken & erbes,” and the name survives in many Germanic languages, including Norwegian and Icelandic. It is a pleasure to look at, with its solitary spreading frond, light green in the spring, darkening later, sometimes covering sunny hillsides. If one is camping out, it is comfortable to sleep on, better than straw, because it absorbs and insulates so well. But it is one thing to sleep on it, admire it, and quite another to eat it, as cattle and horses sometimes do when the tender young shoots come up in spring. Animals that eat bracken may develop the “bracken-staggers,” because bracken contains an enzyme, thiaminase, which destroys the thiamine necessary for normal conduction in the nervous system. As a neurologist, this intrigues me, for such animals may lose their coordination and stagger, or show “nervousness” or tremor, and if they continue to eat the bracken, they will get convulsions and die.
But this, I now find, is only a tiny part of bracken’s repertoire. Robbin calls bracken “the Lucrezia Borgia of the fern world,” for it packs a series of horrors for the insects that eat it. The young fronds release hydrogen cyanide as soon as the insect’s mandible tears into them, and if this does not kill or deter the bug, a much crueler poison lies in store. Brackens, more than any other plant, are loaded with hormones called ecdysones, and when these are ingested by insects, they cause uncontrollable molting. In effect, as Robbin puts it, the insect has eaten its last supper. The Romans used to cover their stable floors with a litter composed mostly of bracken. In one such stable, dating from the first century, 250,000 puparia of the stable fly were found, almost all showing arrested or perverted development.
And—as if all this were not enough—bracken also contains a powerful carcinogen, and though cooking destroys most of the bitter tannins and the thiaminase, humans who consume large quantities of bracken fiddleheads over long periods are more apt to develop stomach cancers. With this fearful chemical arsenal, and its aggressively spreading, almost unkillable, deep-underground rhizomes, bracken is potentially a monster, capable of carpeting huge areas of ground and depriving all the other ground-cover plants of sunlight.
But the bracken here, Pteridium feei, is gorgeous, and—unlike the common brackens—it is quite rare and special, an endemic species confined to southern Mexico, Guatemala, and Honduras.
Tomorrow, on the Atlantic slope, John promises, we will see a species of Pteris—a generic name confusingly similar to Pteridium, but a quite distinct genus and family; we will see the magnificent Pteris podophylla, which has most unusually constructed fan-shaped fronds ten or twelve feet in length. John has been effusive, almost lyrical, about its giant “pedate” fronds, so I decide to read up on it in his Flora. But looking up P. podophylla, I get waylaid by a description of another Pteris, P. erosa, which John and his colleague Joseph Beitel discovered on their Oaxaca expedition in 1971. What astounds me most here, is to see that their description in English is preceded by a paragraph in Latin: “Indusio fimbrato, rachidis aristis 1 mm longis necnon frondis dentibus marginalibus apicem versus incurvis diagnoscenda.” When I ask John about this, he explains that whenever a new species is discovered or claimed, its formal description, its diagnostic criteria, has to be, by tradition, in Latin. I knew that this had been the case centuries ago, in zoology and mineralogy as well as botany—but only in botany has this strange, medieval habit persisted.
Having ferned for an hour, we take a break for our lunch and I eat, unwisely, quite an enormous meal (the altitude—we are at 9,000 feet—has given me an appetite). A sandwich, two sandwiches, a third sandwich, dessert, and a couple of beers to top it off. Then we troop back into our bus and backtrack, just a couple of miles to a side road. This little road, John tells us, is exceedingly beautiful, passing through an epiphyte-hung forest to a limestone outcropping with a great range of ferns. We start walking briskly along the road, which winds up to almost 10,000 feet—too briskly for me, I start to realize, because I have begun to feel rather ill. My large meal, the gaseous beer, has blown up inside me, and as the road climbs I feel short of breath. My heart is thumping, a wave of nausea comes over me, I break out into a cold sweat. Altitude sickness, plus the folly of a large meal. “Take it easy!” someone remarks as they stride past me. I may be reasonably fit, I think, but I am sixty-six years old, and not yet accommodated to this altitude. I have a sense that the blood is draining from my head, and that my face, if there were anyone to see it, has gone quite gray. I would like to stop and rest, but feel I must hurry to keep up with the others. The nausea grows worse, my head pounds, I start to feel dizzy. Part of me says it is nothing, it will pass; but another part of me is becoming intensely anxious, and suddenly I am convinced that I may die here and now, so I sit down abruptly on a boulder, panting for breath, no energy even for making notes. I will reconstruct the afternoon’s activities when I return to the hotel this evening.
* Most of the world’s plants—more than 90
percent of the known species—are connected by a vast subterranean network of fungal filaments, in a symbiotic association that goes back to the very origin of land plants, 400 million years ago. These fungal filaments are essential for the plants’ well-being, acting as living conduits for the transmission of water and essential minerals (and perhaps also organic compounds) not only between the plants and fungi but from plant to plant. Without this “fragile gossamer-like net” of fungal filaments, David Wolfe writes in Tales from the Underground, “the towering redwoods, oaks, pines and eucalyptus of our forests would collapse during hard times.” And so too would much of agriculture, for these fungal filaments often provide links between very different species—between legumes and cereals, for instance, or between alders and pines. Thus nitrogen-rich legumes and alders do not merely enrich the soil as they die and decompose, but can directly donate, through the fungal network, a good portion of their nitrogen to nearby plants. United by these multifarious underground channels (and also by the chemicals they secrete in the air to signal sexual readiness or news of predator attack, etc.), plants are not as solitary as one might imagine, but form complex, interactive, mutually supportive communities.
* I must have misheard the name, for when I asked the others later what “Civocarpus” was, none of them had the foggiest idea.