A Garden of Marvels Page 8
Two weeks after pollination your ward will be the size of a basketball. Two weeks after that, it will weigh four hundred pounds. (By this time, you ought to have shoveled some sand under your burgeoning fruit to prevent it from rotting on the underside.) According to the Engineers Guide to Supersizing Pumpkins at Impactlab.com, the bigger a gourd gets, the more physical stress it experiences, which triggers it to grow even more. “Their weight generates tension, which pulls cells apart and accelerates growth,” writes David Hu at the Georgia Institute of Technology. At around 220 pounds, your round pumpkin will start to flatten under the pressure of its own weight, which is why it will ultimately look like a Brobdingnagian orange pouf rather than a humongous orange orb.
Starting in June, you’ll need to shelter your protégée from the sun. The danger is that as your pumpkin packs on weight—up to forty pounds a day in midsummer—its sun-toughened skin will crack under the pressure of its rapidly expanding innards. Steve uses a wooden structure covered with a lightweight, white fabric as a sunscreen; others pile on white towels. Still, sometimes pumpkins explode. It’s a sad day when it happens, but you know what they say about making omelets.
But for all the drama and action in the pumpkin patch, the most significant factor in growing a record-breaker is not how you care for the giant vines, leaves, and fruit that you see, but how you care for the roots that you don’t. Not surprisingly, soil preparation is an obsession for the most competitive giant pumpkin growers. Champion Len Stellpflug adds five cubic yards of manure—weighing several thousand pounds—to his patch near Rochester, New York. The best manure is a subject of intense debate: Some growers swear by chicken manure mixed with sawdust while others add cow, horse, or alpaca poop. Manure happens, but minerals may not. Providing just the right mix is essential. In addition to sixty pounds of kelp and fifty pounds of humic acid, Ron and Pap Wallace added more than 220 pounds of calcium, manganese, potassium, sulfur, and magnesium, with a soupçon (relatively speaking) of 20 Mule Team Borax, and that was all before June. Serious competitors send a leaf sample to be tested for nutrient analysis every two weeks, and amend their soil accordingly.
An Atlantic Giant is about 90 percent water, so getting enough water to the roots is essential. Some growers use drip irrigation systems; others a combination of sprinklers, misters, and hand watering. Deep into a New England summer they may have to add as much as 125 gallons a day to the ground. Some growers warm the water first in a polypropylene outdoor tank. This is not as silly as it sounds: The theory is that cold water sends a signal to the pumpkin that winter is coming and it should stop growing. Other midsummer techniques that growers use, like massaging their tender baby with oil or bathing it with milk, are more suspect.
Ample water and perfect soil are meaningful only if your pumpkin has a healthy, well-developed root system to take advantage of them; the source of big fruits is big roots. This is why, throughout the season, growers dig a little trench ahead of their vines and lightly bury each one as it creeps forward. At every leaf axil (as well as at root tips and throughout the cambium) is undifferentiated cell tissue called meristem. Axillary meristems are capable of forming a bud for either a new leaf, a flower, or a root, depending on what chemical signals they receive. If you bury the axils, they will produce new taproots, which then send out lateral roots that channel more water and nutrients back to your gourd. The laterals, however, are fragile and run shallow, so most growers lay down wood planks around their patch so they won’t inadvertently crush these delicate pioneers. But should you spot a man or woman tending their pumpkins on snow skis, don’t be surprised. They believe their skis spread their weight and allow them to pass especially lightly over the soil. In Giant-Pumpkin Land, the road to hell is paved with wood indentions.
eight
The Way of All Water
No doubt, eight thousand years ago the farmers at Catal Hüyük in modern-day Turkey understood that roots had something to do with feeding and sustaining their emmer crop. They could hardly have missed the fact that emmer, the antecedent of modern wheat, grows better in dark, loamy areas than sandy ones and that plants in dry soil go limp and die. Ancient Egyptians certainly knew that without the summer flooding of the Nile and a new coating of silt on the land, there would be poor crops in the spring and famine the following year.
How roots gather food from soil and distribute it throughout the aboveground part of the plant was, however, a deep mystery. Aristotle believed roots took in food from the soil indiscriminately, and concluded that whatever that food was, it was ready to be consumed because he found no stomachlike organ in plants. Theophrastus disagreed: Roots could choose what to take in and had a digestive capability. Eighteen hundred years later, the question was still open. One of the few to write on the subject, the renowned Renaissance physician Girolamo Cardano, concluded that digestion does take place in the plant, but not in the roots. The stomach of the plant, too small to be seen, must be at the base of a plant’s stem or a tree’s trunk, just above the roots.
That the presumed location of the imaginary stomach is equivalent to the position of our stomach and intestines, which lie at the base of our trunks just above our (root-shaped) legs, is no coincidence. Cardano’s plants-to-humans analogy was instinctual, but also encouraged by the prevailing paradigm of the Great Chain of Being. The Great Chain was conceived in the ancient world and exquisitely refined in the Renaissance. It was the model of the relationship among all the world’s living and nonliving entities. Imagine the Chain hanging from heaven, with perfect God at the top, the angels below Him, Man just below the angels, and, descending in order of their ever-greater imperfection, the animals, birds, sea creatures, plants, minerals, and finally, stones. Philosophers gave considerable thought to the fine gradations of the hierarchy: Robins, for example, were higher on the Chain than sparrows because robins eat worms (as animals eat meat) while sparrows dine only on seeds. Plants stood higher than minerals because, like animals, they could eat and minerals could not. Plants’ digestive organs would certainly reside in their lower torsos.
In the seventeenth century, discoveries about human anatomy seemed to shed new light on vegetal alimentation. Until that time, people believed that human and animal livers produce cool, venous blood while hearts produce warm, arterial blood, and the two kinds of blood never mix. In 1628, William Harvey proved by experiment that all blood travels in a continuous circuit from the heart through arteries and back via veins whose tiny valves prevent it from flowing backward between pulses. In 1648, Jean Pecquet, a French physician, found that a milky fluid he named chyle leaves the intestines via a lymph duct that connects to a vessel near the heart. Chyle then enters the bloodstream. With these two new facts, a revised theory of human nutrition was born. The heart and the arteries “cooked” the chyle and distributed this food to the body through arterial blood. The blood then returned to the heart, darker and depleted of nutriment, via the veins.*
These discoveries inspired a parallel theory of plant nutrition. What if sap was the equivalent of our chyle-fortified blood? What if sap picked up raw nutriment from the soil, and then circulated it continuously throughout the plant’s body? Now, certain observations made sense. People had long known that if you cut into the outer wood of a tree or sliced through the stem of a nonwoody plant, rising sap flowed out. In the 1670s, Malpighi, in conducting one of his few experiments, added new evidence to the discussions of circulation. He girdled a tree, cutting through only the bark and not into the wood, and discovered that the bark above the cut swelled and the bark below the cut died. Clearly, he had interrupted some kind of downward flow of liquid.
The conclusion was inevitable: Sap flows upward in vessels under the cambium, turns around in the leaves, and seeps down on the outside of the cambium just beneath the bark. Both Grew and Malpighi had seen the vessels that carry fluid upward, which we know as xylem. Grew also managed to observe a tracery of tiny “pipes or tubes” on the underside of bark, vessels we now know as phloem.
There was additional, circumstantial evidence for the circulation of sap. The liquid flowing upward is more forceful and deeper in the tree’s body, just as arterial blood is; the return flow is weaker and closer to the tree’s “skin,” just as venous blood is. Score another one for the model of the Great Chain of Being: Plant sap circulates like animals’ blood, just more simply.
The facts didn’t all fall into place, however. It was perplexing that sap didn’t seem to flow in all seasons. Nor did anyone see capillaries similar to those that Malpighi discovered in animals that connect the upward flow with the downward seepage. (And, although no one seems to have asked the question, what about nonwoody species with the vessels scattered throughout the parenchyma? Their phloem are bundled with xylem in the interior of the stem, and so were invisible to observers in this era.) But the biggest problem with a theory of a vegetal circulatory system was that a plant had no heart, no engine for pushing fluid up and around.
Many solutions to the problem were proposed. Claude Perrault, a French scientist and architect, suggested that as branches swayed in the wind they compressed the sap vessels, pushing the fluids inside. Grew offered that the little “bladders” he saw in the parenchyma were cisterns for sap, which swelled and squeezed fluid into and through the vessels. (Those little bladders are actually living cells that store sugars and have other functions, depending on their location in a plant.) Malpighi thought the “spiral vessels” he saw wrapped around xylem expanded in the heat of day and contracted at night, squeezing the liquid along its way. (The spiral elements he saw are actually thickenings of the xylem walls that help keep them rigid.) Despite the lack of a consensus on what force impelled sap to circulate, no one doubted that circulate it did.
Not until 1715, did someone finally test the proposition. That someone was the Reverend Stephen Hales, a curate in the English village of Teddington. Hales was the youngest son of a baronet in the county of Kent. He earned his M.A. in divinity at Cambridge in 1703, and then took up a fellowship while he waited for the current occupant of his promised curacy to move on to the greenest of all pastures. Without any duties and at loose ends, this intellectually curious young man befriended an undergraduate medical student, and tagged along with him to his classes.
The goal of the university continued to be, as it had always been, to educate the next generation of ministers, lawyers, and doctors. Most experimentation and research in England at that time took place at the Royal Society and in the home laboratories of wealthy amateurs, not in classrooms. But the university was beginning to offer courses beyond the traditional ones in Latin, rhetoric, logic, moral philosophy, ethics, and basic mathematics. A new observatory had been built on the top of the Great Gate at Trinity and the first chemistry laboratory—although the chemistry was not much more than alchemy—had been constructed on the college’s bowling green. For the first time, science lectures incorporated demonstrations, a profound pedagogical innovation. Hales attended these, and found instruction in the new subjects of hydrostatics and pneumatics. He dissected dogs and cats and made lead casts of their lungs, watched electrical experiments, repeated Robert Boyles’s air-pump experiments, and designed an orrery based on Isaac Newton’s understanding of the solar system.
Newton strongly influenced Hales, although the professor had left Cambridge in 1696, the year Hales matriculated, to take over the operation of the Royal Mint. In fact, it was only after Newton’s departure that students were taking courses based on his discoveries and his great works, the Principia, Optics, and Arithmetica universalis. When Newton had been on the faculty, only a few students attended his lectures, and the great man spent most of his time working alone on his physico/mathematical theories and his alchemical experiments. (It was said that as he walked the garden paths at Trinity College, cogitating, he drew diagrams in the gravel that everyone reverentially stepped around.) Hales absorbed the Newtonian model of the natural world, the new model that was beginning to supersede the older, Cartesian one.
René Descartes, who died in 1650, had been a revolutionary thinker in his time. He had rejected the ancient and still prevailing belief that natural objects—and even the universe itself—had souls that animated them, which explained why apples fall down to earth and plants grow up. No invisible forces, which to Descartes and his rationalist cohorts meant occult forces, were needed to explain the motions of matter. Instead, he posited a clocklike universe that once set in motion by God ran on its own in perpetuity without further interference on His part. In the Cartesian model, all motion was communicated from one part of matter to another by direct contact, the way gears in a clock’s workings engage and turn each other. It was Newton’s insight that unseen forces do play a role in determining the motion of matter. He could not explain how gravity, magnetism, and cohesion draw and repulse matter across empty space, but he knew the forces are real, measurable, and, above all, operate according to mathematical laws.
By the time Rev. Hales took up his curacy in early 1709, he was thirty-one years old and had become a thoroughgoing Newtonian. Like Grew and many other English scientists of his time, he also saw no contradiction between his religious beliefs and scientific interests. As he would write in his first book, “Not only the grandeur of this our solar system, and the other heavenly bodies, declare the glory of God, but also the exceeding minuteness of microscopial animals, and of their component Parts.” So, it was with a clear conscience that once installed at Teddington, he launched himself simultaneously into his ministry and a program of natural experimentation. Newton had measured the forces that governed the movement of objects; Hales, more modestly, set out to measure the forces of the circulatory system of animals.
Teddington was a quiet village with a population of four hundred about fifteen miles outside London. It was home to a single church and two inns, and was surrounded by hundreds of acres of open, low-lying fields bordering the Thames River. For many of Hales’s parishioners, a scientifically minded curate must have been a curiosity, although if his focus had been astronomy or classifying plants, his passion would have gone with little comment. That his particular scientific interests made a strong impression is not surprising. In one of his early experiments, he tied a struggling white mare to a gate laid on the ground, squatted to cut a hole in her left carotid artery with a pen knife, and, by then surely blood-spattered, inserted the end of a twelve-foot-long glass tube into the hole in order measure the force of her beating heart. While he conducted his small-scale experiments inside his garden laboratory, when a Cambridge-educated curate slaughters in his yard some five dozen oxen, cows, deer, dogs, and sheep by sticking glass tubes in their veins or lungs, word gets around. His penchant for vivisection made him quite a notable character in the neighborhood. Thomas Twining, a minister and classics scholar who lived nearby, would later write of
Green Teddington’s serene retreat
For Philosophic studies meet,
Where the good Pastor Stephen Hales
Weighed moisture in a pair of scales,
To lingering death put Mares and Dogs,
And stripped the Skins from living Frogs.
The poet Alexander Pope, who also lived in the area, was quoted as saying of Hales that “[I] always love to see him, he is so worthy and good a man. Yes, he is a very good man, only I’m sorry he has his hands so much imbued in blood.” Blood, however, was at the core of Hales’s research.
Despite his odd and sanguinary interests, the reverend was popular in the parish. He was blessedly undogmatic, and his sermons emphasized God’s goodness and the need for ordinary charity. (On the subject of extramarital relations, however, he was strict, requiring those guilty of adultery and fornication to wear the customary white robes to church and beg forgiveness from the assembled congregation.) He generally avoided the doctrinal issues that had ignited civil war in the previous century and continued to rive the Protestant community. Attendance at St. Mary’s Church increased after his arrival, and the church had to be enlarged in 1716
to accommodate his growing congregation.
In 1715 or so, Hales suddenly diverted his attention from quantifying the flow of blood in arteries and veins to studying the passage of sap in plants. Like Malpighi, he may have hoped that the study of plants would illuminate the workings of animals. Certainly, it was far easier—and more socially acceptable—to cut up cabbages than cats. In 1718, he read his first paper at the Royal Society, reporting “a new Experiment upon the Effect of the Sun’s warmth in raising the Sap in trees,” and was promptly elected a Fellow. The Society urged him to continue his work, and in 1727 he presented his groundbreaking treatise, titled Vegetable Staticks.
Hales used the word vegetable, as everyone did, to mean all of plant life. By staticks he meant both measuring in general, but also specifically the measuring of the input and output of fluids, as well as their force and speed. One of the first questions he addressed was whether sap does in fact circulate, like blood in an animal, through a closed system. If it did, he reasoned, it would flow in one direction only, just as blood does.
To test the theory, he cut off a leafy branch of an apple tree, removed the tip of the branch, then put the branch upside down in a glass tube of water. The tube was connected to a denuded branch placed upside down in a bucket of mercury. (See Figure 13 on the next page.) On a sunny day, the leafy branch emptied the tube of water and drew mercury up toward the denuded branch, proving water could pass easily in the opposite direction of its normal flow. Stripping the branch of bark made no difference to the results. Finally, he tried the experiment with a living branch. (See Figure 14 in the following illustration.) Sap, he correctly concluded, does not circulate like blood.