A few weeks later, I was studiously avoiding the plaza in front of the museum. I feared the worst. I wanted to delay the hour of doom. I was checking some trees we’d planted on upper Fifth Avenue, when I got a call from a client down in the 60s on Fifth. She is always worried about her fine katsura trees. Trundling down the road, I suddenly realized that I was abreast of the pollard plaza at the museum, and there, on two trees nearest me, I could see tiny light green shadows at the edges of the knuckled stems.
I slammed on the brakes and pulled to the curb. Could it be true? There is no parking in front of the museum. I was not parking, I reasoned. I was “loading and unloading.” I was taking a tremendous load off my mind. I tried to walk nonchalantly toward the fuzzy-ended planes, though to a stranger it may have appeared like an eyes-closed rush.
There they were: Yes, they were leaves. Yes, there was more than one of them. Yes, there were numbers of leaves emerging! Yes, they were emerging on each and every—or almost each and every—stem. “Say Amen!, somebody!” I breathed. I felt like my old friend and boss, then the dean of the Cathedral of St. John the Divine, who, whenever he found a parking place in Midtown Manhattan, threw up his hands and exclaimed in jest, “There is a God!”
I was excited to touch them. I felt something like what Thoreau must have felt when he first saw the acres of sprouts coming up from an oak wood that he had recently burned. Like the native peoples before him, his people had still cultivated some of the woodland by fire coppice: by burning and letting grow again. “How beautiful the sprout-land (burnt plain) seen from the cliff!” he wrote. “No more cheering and inspiring sight than a young wood springing up thus over a large tract, when you look down on it, the light green of the maples shaded off into the darker oaks; and here and there a maple blushes quite red.”
I had not scorched the London planes, but I had certainly whacked them. I shared the feeling of inner renewal that Thoreau drew from the sprout’s persistence. “Shall man then despair?” he continued. “Is he not a sprout-land too, after never so many searings and witherings?” No doubt about it. As I hurried back to the car before it flowered with traffic summonses, there was a sproutish spring in my step.
I began to trust in the power of sprouting, and the more I learned, the more I came to believe that trees are more perceptive, more intelligent, more generous, and more persistent than we are. We could learn from what they knew and what they did. Thoreau saw them as clearly as anyone ever has. “If you examine a wood-lot after numerous fires and cuttings,” he wrote, “you will be surprised to find how extremely vivacious are the roots of oaks, chestnuts, hickories, birches, cherries, etc. The little trees which look like seedlings of the year will be found commonly to spring from an older root or horizontal shoot or stump.” Commonly, indeed. In a review of the literature on sprouting among leafy trees, Arnold Arboretum botanist Peter del Tredici estimated that 80 percent of trees in a broadleaf forest are not seedlings but sprouts from a preexisting stem.
Woodlands are sprout lands. Scrabbling in the dirt, Thoreau looked at young trees. One four-year-old red oak about a foot high rose from an acorn an inch beneath the pine-needle duff. It had already died back once and sprouted again. A black oak of about the same age was only six inches tall and much branched, having been chewed down by rabbits at least once. The stem was just a quarter inch in diameter, but the root beneath it in the soil was three times fatter. The tree was storing up the will and the food to grow or to sprout again. Another taller white oak stem, maybe seven years old, had also shot up again after a rabbit had eaten it down. “These little oaks in their earliest years,” he observed, “are forming great fusiform vigorous roots on which they can draw when they are suddenly left to seek their fortunes in a sprout-land.”
Some trees can grow again from the base indefinitely. Most conifers can do so only when they are seedlings, but ever after if their branches hit the ground, the tips can root again. Leafy trees can sprout from the base for at least fifteen or twenty years, many of them for half a century or more, and some for as long as they live. Sprouters that make clonal groves—like quaking aspens or the Tasmanian Lomatia—can in theory keep sprouting forever (see page 291).
There are trees that possess a lignotuber, a specialized organ at the base that maintains viable dormant buds for the entire lifetime of the tree. Lindens all have lignotubers. They sprout promiscuously, causing arborists headaches, because we must explain to our client that the tree is not dying, just vivacious. When you find a multistem basswood in the forests in the Northeast, it is very likely the result of many stems that sprouted from the lignotuber when the previous tree died. It is a kind of natural coppicing. The flare at the base of each tree is a colony of buds, ready to recruit new stems. The word “recruit” itself comes from the French meaning “to grow again,” referring to the ability of trees to sprout after cutting. It was an ironic way to speak of armies as being indefinitely refillable.
To branch and branch again was no innovation, not something trees learned to do because of an Ice Age or some other recent perturbation. It was rather a way of life that they had gradually perfected over 400 million years. Back in the early Silurian, before plants came on land, the seaweeds had learned to fork as they grew. Each stem had sprouted two daughter stems. Each daughter had done the same. And so on and so forth, ad infinitum. In this way, a single plant had been able to spread across the surface of the water, exposing as much of its green surface to the sun as possible and so making by photosynthesis the most food that it might.
These branches had been leafless. All the tissue of each stem had been green—suffused with chlorophyll—and all of it had made food out of sunlight, water, and carbon dioxide. (Still today there are some trees—sassafras, box elder, and sweet bay magnolia are three—whose youngest stems are green and photosynthetic.) The surface of the water had been the roof of their world. Growing up had not been an option, since the roof had contained them, but spreading out across it had been a big help. It had been as though the vegetable world were growing in some enormous conservatory under glass. The stems had multiplied, feeling at the upper edge of their world, like hands exploring a glass ceiling—only these hands had made food and so had given rise to more hands.
Now and again, an alga had broken from its holdfast, and washed up on shore. It had dried out, but likely not before it had been attacked by terrestrial fungi, among the earliest land creatures, whose branching hyphae had woven in and out among the plant cells and digested the remains. In this way had come early dirt, a new creation forged from broken rock, clay, and the mineralized remains of the dead. Again and again, many thousands of times, however, a fungus had been slow on the uptake. It had fed on nitrogen from the alga’s cells while still attached to and feeding on the detritus in the dirt. The water and minerals it had absorbed from the soil had leaked into the tissues of the plant. The plant could stay alive, because the parasite now gave it what the sea had given it before. The fungus had got its food, not only for a moment, but for as long as the plant could stay alive. The two had acquired a common interest. Roots had been born.
This proto-plant might have simply sprawled across the land. Indeed some did. They looked rather like guts, oozing in bulbous lobes over the shallows and the rocks. The plant’s fungal roots gave it the water it needed to survive. Each organism had a core of hardened tissue, the aptly named sclerenchyma, that both channeled water to the green photosynthesizing cells and gave a bendy backbone to the stem.
One year, a plant stood up. Its descendants—that is, every tree and shrub—eat by acclamation. They raise their hands to the sky. For many years, many decades, even centuries, and in principle eternally, a woody plant can hold up and out its continually self-renewing leafy branches. Goethe derived the whole plant from the leaf. As he saw it, the root, the stem, the twig, the flower, and the fruit all arose as modifications of the leaf. From the spleenwort to the redwood, it was all one idea, elaborated, adapted, ramified, repeated. Once the roof of the conservatory was removed, only the height of the atmosphere and the load limits of standing wood could contain the upward growth.
It was a wonderful way to understand growth and form, because it worked not from arcane cellular and subcellular minutiae, but from observations of whole living plants. Recent morphologists—scientists who look at form for clues to the life history of creatures—think it was the stem, not the leaf, that came first, but they honor Goethe’s method. The German poet and scientist had called his great work The Metamorphosis of Plants. In the telome theory, botanist Walter Zimmerman and his colleagues distinguished four metamorphoses that they believe gave rise to trees and shrubs, and eventually to all living plants. The four are overtopping, flattening, webbing, and reduction.
According to the telome theory, woody plants were originally dichotomous, each branch dividing into two equal daughters. Soon, one branch overtopped another creating a leader with lateral branches. Then, groups of laterals flattened into a plane. Webbing grew among the flattened twigs, giving rise to the first leaves.
The story as they tell it is about learning to branch, to leaf, to flower, and to fruit. Once there was a sprout. It stood up on the land. It was glad because now it could expose all of its aboveground surface, not just the top side, to the light. It strained upward toward the sun. It did just as its waterborne cousins had always done. One branch forked into two equal daughters, only now there was no roof over their heads. Each shot up into the sky. One got a little more light than the other, so it grew a little faster and a little taller. It overtopped its sister, so the little sister moved its growth out sideways, where it too could get enough light. Here was the distinction between a lateral branch and an upward-leading branch. Then it rested.
When growth began again, the two daughters each forked, each making two granddaughters. Again, on each, one overtopped the other. One granddaughter on the tallest stem continued to grow upward. Again, the slightly weaker sibling branched off to make her way. On the weaker of the original daughters, one granddaughter might get uppity and turn upward to compete with the rising leader, or both it and its sister might just fork wider, seeking their way to the sun in spreading extension, not vertical erection. Still, one grew more than the other, so the branch extended outward at its angle. Season by season, the new growth continued in this way, the leader zigzagging into the sky, and the lateral branches zigzagging outward and upward, a compound gesture of acclamation, increasing as the plant grew taller. You can still see today this zigzag habit in the twigs of some trees like the sycamore, hackberry, linden, and beech.
This way of growing harvested more sunlight and made more food. The plant was emboldened. What if instead of zigzagging, it just grew straight up? With each new season, one daughter would begin life as the upright leader, and two or three more would start out as lateral branches. Look at the top of a spruce or a young white pine. It shoots up straight as an arrow with its laterals fanning out at angles beneath it. As it branched and rebranched, the plant could be more sure that each of its new daughters would find her slice of sun. The bud developed as a branch in embryo, protected by hardened leaflets. Year by year, a new season would release the new buds at the tips of the youngest branches, continuing the pattern of growth.
Life could be even surer with another metamorphosis. Some successive ranges of branches, subbranches, branchlets and twigs might grow in a single plane. To be sure, not all of the branches of the tree should do this or it would sacrifice 340 degrees of the circle. But if close-fit groups of lateral branches or their branchlets flattened into a single plane, many more sprays could orient themselves to reach the light. Walter Zimmerman called this planation—that is, the flattening of sprays of daughters and their progeny.
A strange thing happened to some of these flattened sprays. When the twigs were near one another, they began to sprout flags or standards of fine thin green tissue. These flags met. They webbed the space between the leader twiglet and its laterals. All of this tissue could use the light to make food. It was the first leaf.
In this story, the leaf is outcome, not origin, as Goethe had claimed, but one can understand Goethe’s love of the leaf form, for through it the power of plants to grow multiplied by orders of magnitude. Through it, the system that powers the uptake of water came to be. The leaf allows plants today to take more than 56 billion metric tons of carbon from the air each year, creating the organic compounds upon which all the rest of life subsists.
When the sprouts were simply forking, the tips did for reproduction, with both male and female organs meeting there. As some stems overtopped others, webbed, and fused, they folded modestly over on the sexual parts and fused into the carpel, closed seed vessels, the spores of ferns, and the stamens of the flowers. They protected and enclosed the reproductive parts by reduction of some growing tips to form vessels for the seeds.
The whole tree is thus woven by the growth and the metamorphosis of its sprouts. A tree is in a forest, but there is also a forest in each tree. Every new branch arises on its parent’s stem in exactly the same way that its first parent arose from the dirt. If you look closely at the trunk of an old tree, you can sometimes see how its largest branches attach to the trunk with fingers of tissue that closely resemble the roots of the parent stem. The great French botanist Francis Hallé called the young branch an epiparasite, because when it is young, it depends upon the existing branches for its food, as did those branches before them. Only as one makes enough of its own leaves does it feed itself and then finally begin to export surplus food to the rest of the tree.
Once it does so, like a maturing daughter, it must fend for itself. If shade or breakage or insects damage it, the branch may die. The rest of the tree will not come to its aid, but the branch may save or restore itself by means of dormant buds, embryonic branches that will never be allowed to grow, except in case of need. This was the greatest innovation in the life of shrubs and trees: They learned to keep spare parts, extras, recruits, not only at the base but on the trunk and branches. Each of these could be called upon in the event of damage or disease to come forth and begin to branch again.
Conifers dominated the early world of trees. Their idea was to start life as green pyramids. They occupied more ground space at the bottom than the top. The base of the tree made elbow room for the crown, so that the slender tops would be more likely to get sun, even were the forest packed with fellow trees. Spare buds were needed not near the base of branches, but at the tips, where they could hit the ground, root, and start a new member of the tribe. Leafy trees, on the other hand, began life fighting for space and light in a world dominated by conifers. They had to be sneaky, and they had to be quick. They kept recruits all up and down each branch, so a new stem could immediately shoot up toward any ray of light.
Tree people have many different names for these extra buds. For some they are dormant, for others suppressed, for still others reserve buds. The names reflect more the variety of human feelings about nature than any difference in the buds themselves. The friendly Rousseauian sees them sleeping, the tough-minded Hobbesian sees them violently quashed, the calculating Adam Smithian sees them as handy spares. They are all of these at once. Trees are much closer to the facts of their nature than are we to the facts of ours. On those branches are many such buds, ready to sprout if needed.
The evolution of tree structure is astonishing, but the really brilliant thing were those spare buds, whether you call them dormant, suppressed, or reserve. Only through them can the plant replace lost leaves, make food, and stay alive. If an ice storm, a big wind, an infestation or disease, or a pruner like me takes down a branch, and if the tree could not then have made a new branch to replace what had been lost, it would have had to go hungry. Each of those buds contains a copy of the tree’s plan, ready to release it should the need arise.
Learning this, I felt more secure about my new-sprouted baby plane trees at the Metropolitan Museum. As the season went on, each of the new twigs from the stubbed ends grew to three feet or more in length, making wonderful wild heads like a hundred fright wigs, and their big sycamore leaves beautifully shaded the tables and chairs beneath them. I felt they were at once indispensable to the tree, beautiful to see, and a delight to sit beneath. I was willing to bask in the glow of our new companionship, though I thought it likely that late in the following winter, when we would have to cut them again, my terror would return.