A Garden of Marvels Page 20
Nehemiah Grew was the first European since the classical era to posit plant sex. The stamen, he suggested in The Anatomy of Plants (1682), just might be the male flower’s generative organ. It was possible that the anther served as “a small penis” and that the “small Particles” produced by the anthers were “Vegetable Sperme.” When the particles fell on the “Seed-Case or Womb” of a female flower, he wrote, they impart a “Prolifick Virtue.” This was astute speculation by a careful observer of plants, but it was conjecture only, and Grew did not attempt any experiment. John Ray, the notable English naturalist, seconded his countryman’s notion, but Marcello Malpighi, equally authoritative, disagreed. He thought seeds develop the way flower buds do. Buds don’t need fertilization to develop, so why should seeds? Pollen isn’t sperm, he wrote, it is excrement.
Grew’s proposal that flowers have genitalia generally went unremarked. It was, after all, only a thought and, for most people, a profoundly unsettling one. Rudolf Jacob Camerer, the director of the Botanic Garden at Tübingen, was one of the few who did take notice. Camerer was a generation younger than Grew and Malpighi. He started his investigation of flowers around 1690 by looking at the development of the embryos inside the seeds of bean and pea plants.
Both these species (and 90 percent of all flowering plants) have hermaphrodite flowers, meaning each flower on a plant has both male and female sexual organs, male stamens and female carpels or pistils. (To remember that stamens are the male organs, think of the “men” in stamen. Carpels and pistils are synonymous for my purpose here.) The stamens are composed of threadlike filaments topped by pollen-producing anthers. The carpels are composed of, from bottom to top, a rounded ovary with ovules inside, a slender style, and a flattened crown called the stigma. Looking through a microscope at the flower of a pea plant, Camerer realized that its ovules are initially filled with clear liquid. After pollination, the volume of liquid decreases in the ovule, and a small green point or globule appears. The globule becomes an embryo with two tiny leaflets (its cotyledons—pronounced ka-tull-EE-duns) and a tiny root and shoot. Camerer realized there had to be a relationship among these events. The flower’s pollen, he hypothesized, fertilizes its ovules, which become the new embryos.
A lily flower.
Camerer ran a series of experiments with mulberry trees and dog’s mercury, a shade-loving plant that carpets European forests, to test his hypothesis. He chose these species because they are among the few in northern Europe that are dioecious (di-EE-shuss), meaning the male flowers grow on one plant and the female flowers grow on another, and so, he reasoned, he could easily eliminate all male plants in a test plot. When he did so, the seeds of his female plants failed to ripen. He then ran similar experiments on monoecious (mon-oh-EE-shuss) plants, including maize, that have separate male and female flowers on the same plant. The two types of experiments proved to his satisfaction that if pollen doesn’t fall on stigmas, either no seeds form or the seeds are sterile. There is, he concluded, no virgin birth in the plant world. Flowers have sex.
No lightning bolt seared him for this heresy, and in 1694, he wrote up his results in a letter to a colleague that was printed in Transactions of the Tübingen Academy. As A. G. Morton noted: “Few epoch-making papers can have had smaller circulations than this famous De sextu plantarum epistola.” Still, how could this data, no matter how obscurely announced, go unheralded?
For one, there was some ambiguity in Camerer’s results. Sometimes a few fertile seeds resulted from his experiments with maize and hemp. (In the case of maize, wild pollen may have drifted into the trial patch and fertilized the seed. As for hemp, it has a quirky sexuality: Generally dioecious, its female plants occasionally produce male or hermaphroditic flowers that can fertilize its female flowers.) There was also the puzzle of club mosses and horsetails. They appeared to have anthers but no carpels, so how could anthers be sexual organs? (What observers thought were anthers were actually sporophytes, organs that release spores.) The bigger problem was that Camerer’s proposition that flowers are sexual was repulsive in the seventeenth century. Besides, one of the world’s most influential botanists, Joseph Pitton de Tournefort, at the world’s premier institute of botanical research, the Jardin du Roi in Paris, was unequivocal on the subject: Anthers were excretory organs. For more than twenty years, little further was written about flowers and sex.
Then, on June 10, 1717, at six o’clock in the morning a sub-demonstrator of plants at the famed Jardin, the forty-eight-year-old Sébastien Vaillant, stood up and delivered “the talk.”
Vaillant was a substitute lecturer for Professor Antoine de Jussieu. Jussieu was a medical doctor, university-educated as all French physicians were, and the son of a well-to-do master apothecary, an eminence at one of the most prominent of the French guilds. The great Tournefort had died in 1708, and Jussieu, although only twenty-two years old, had succeeded to his professorship in botany. On the occasion of the inauguration of a new garden, he had been scheduled to deliver a lecture, but at the last minute had to travel to Spain. Vaillant, an older but more junior man at the institution, was chosen to speak in his stead.
Vaillant was an anomaly as a professional at the Jardin. His colleagues were all men of the nobility or the haute bourgeoisie, but he was the fourth child of a tradesman in northern France. When he was six, his father had boarded him with a priest who had given him religious instruction and taught him to read and write in French and Latin. Sébastien proved an excellent student and was musical as well, and his father scraped together the funds for harpsichord and then organ lessons, hoping his talented son might make a living as a church organist. At the age of eleven, the boy became the organist both at the cathedral in Pontoise and, in exchange for room and board, for the nuns at a nearby convent.
The nuns allowed their little musician to trail along with them when they worked at a nearby hospital, and Sébastien often slipped into the surgical theaters to watch the operations. Surgery fascinated him, and the surgeons, taken with his interest, loaned him books and—in an early and remarkable example of hands-on science at the elementary school level—gave him human body parts to dissect in his own room at night. Soon, he had taught himself enough to be accepted as an apprentice. He needed no academic training: Surgeons, affiliated with those other knife-wielding specialists, the barbers, were considered tradesmen. At twenty-one, with his apprenticeship completed, Vaillant moved to the suburbs of Paris to find work.
The move gave him the chance to attend public lectures at the Jardin du Roi in medicine and botany, those intertwined subjects. Here, he found his calling. He met Tournefort, and joined the other students who attended the renowned professor on his weekly field trips outside Paris. Vaillant took detailed field notes and wrote up descriptions based on his observations and, given that he was so handy with a knife, his meticulous dissections. The director of the Jardin, the noble-born Dr. Guy-Crescent Fagon, was impressed by his work and hired Vaillant to be his secretary, as well as the keeper of the Jardin’s herbarium, or dried plant collection. When Vaillant was thirty-nine and an acknowledged master of plant anatomy and taxonomy, Fagon also appointed him as director of plant culture (in which capacity he introduced the first greenhouses to the Jardin) and “sub-demonstrator of plants,” a position that entailed explaining the cultivation of plants and their uses to medical students and other garden visitors. The multiple appointments were necessary to provide Vaillant a living wage since the salaries of these positions were honoraria, appropriate for financially independent appointees. Of course, a professorship was out of the question for a mere surgeon.
After Jussieu departed for Spain, Vaillant posted the name of his upcoming lecture: “Discours sur la Sexualité des Plantes,” which meant that the amphitheater on the morning of June 10 was packed. Flowers, Vaillant first declared, were the most important parts of plants. Stamens, which the celebrated Tournefort regarded as the lowest and most vile organs of plants, are actually “their most noble.” Then he got dow
n and dirty. Stamens are responsible, as in male animals, for the reproduction of the species. Their anthers are equivalent to testicles. In dioecious plants, he said, where the male flowers are at a distance from the females, “the tension or swelling of the male organs occurs so suddenly that the lobes of the bud are forced open with surprising rapidity. These male organs, seeking only to satisfy their violent transports, upon finding themselves freed, produce an abrupt general discharge, a swirl of dust, spreading fecundity everywhere. [Then] they find themselves exhausted.” When a flower contains both male stamens and female pistils, “the stamens need not act with such haste or vigor, and . . . it may be presumed that the slower their actions are, the longer will be the duration of their innocent pleasures.” All this, he said, could easily be observed in Parietaria, for example, in the mornings, but if one should happen to miss the action, there was an alternative. Provided “the plants, so to speak, have reached competent age,” they could be spurred into action with the tip of a pin. In either case, the dust flies toward the female organs, where its “volatile spirit” travels down the solid style to fertilize the egg in the female’s “belly.” And so he continued in a scandalously anthropomorphic fashion.
The medical students loved the lecture: Not only was it prurient, but the lecturer had poked a middle finger in the collective eye of the stuffy establishment, always a thrill for the younger generation. Vaillant clearly enjoyed his subversive moment on the stage. He had long felt that Tournefort’s major opus on classification, a new edition of which Jussieu was in the midst of preparing, was inadequate, but he had been unable to convince his superior to make any changes. Never had he doubted that he was the equal or better of Jussieu, despite the professor’s elevated social and professional status. Surely it was a great pleasure to speak his mind and oppose conventional wisdom. I imagine he felt as liberated as those exploding anthers that morning.
Jussieu, on his return, was outraged. The lecture was an affront to the authority of the Jardin; the students’ demands for more lectures from Vaillant were personally insulting. The French Academy of Sciences, shocked at the criticism of Tournefort, refused to allow the “Discours” to be published in France. The lecture might have gone the way of Camerer’s letter, but Vaillant had friends outside France, the English botanist William Sherard and Professor Hermann Boerhaave at the University of Leiden, and they saw to its publication in both French and Latin. Not long after, Vaillant would write to Boerhaave, with relish, that “our lecture has created a real fracas here.”
The lecture became famous. In 1725, when Carl Linnaeus was a student in Sweden, he absorbed its gist and spirit. “The petals of the flower,” he wrote, obviously influenced by Vaillant, “in itself contributes nothing to generation, but only serves as the bridal bed, which the Great Creator arranged so beautifully, and garnished with such precious bed-curtains, and perfumed with so many delicious scents, in order that the bridegroom with his bride may therein celebrate their nuptials with so much greater solemnity. When the bed has been so prepared, it is time for the bridegroom to embrace his darling bride, and loose himself in her.” Linnaeus would become famous for establishing the convention of binomial Latin names for plants and animals, as well as the “sexual system” for classifying plants. His system, first presented in Systema Naturae in 1735, was based on the details of a flower’s sexual anatomy, including the number of stamens and carpels and their relative positions inside the petals. It was an admittedly artificial classification method, not a natural one based on the totality of traits shared among species, but it was simple and easy. It also solidified acceptance of plant sexuality.
Vaillant was lucky to have already been elected to the Academy before his lecture. Certainly, he would never have been approved afterward. When he died in 1722, the Academy declined to issue the traditional “éloge” for its departed member. If only Vaillant had lived another twenty years, he would have had the last laugh: Linnaeus’s classification system, based on plants’ sexual organs, completely eclipsed Tournefort’s.
twenty-two
Who Needs Romeo?
By the mid-1700s, most botanists agreed that flowers had male and female organs and engaged in a sexual exchange, but the mechanics of the process were a complete mystery. How exactly did pollen “fecundate” a flower’s ova and create fertile seeds?
There was no analogizing from the anatomy and behavior of viviparous (live-bearing) animals: No one had yet seen any sort of eggs or seeds in mammals’ ovaries. (Karl Ernst von Baer would spot the first mammalian ovum in a dog in 1825 and the first human ovum in 1827.) Chickens and ducks and other oviparous (egg-laying) animals seemed to offer the most germane models of reproduction. Semen from roosters and ganders was obviously involved in engendering viable offspring. Exclude the males from the henhouse and you got eggs to eat; let them dally with the females and you got chicks. But how could semen have a fecundating effect when eggs have an impermeable shell?
When it came to plants, there was an additional mystery. Birds have a cloaca, a cavity that leads to the urinary and fecal tracts, and, in the case of females, also serves as a pathway for semen to the uterus. But if pollen were the equivalent of semen, then how, after wind dropped it on the stigma of a pistil, did it get to the ovary to impregnate an ovum? The style looked as if it should be a cloacal passageway, but on examination under a microscope it proved to be solid. Pollen grains can’t fall down the style.
If semen couldn’t penetrate an eggshell and pollen couldn’t pass down a style, then, people reasoned, some nonphysical force of semen and pollen must do the impregnating. According to the esteemed William Harvey in 1662, “it is certain that the semen of the male . . . carries with it a fecundating power by a kind of contagious property, [working] in the same way as iron touched by the magnet is endowed with powers and can attract iron to itself.” Other observers wrote of a “volatile spirit,” a “germinative spark,” or an “aura seminalis” that operated on the egg.
No one had trouble believing that the contribution of semen or pollen was of such an ineffable nature. In fact, it was hard to see why a male was needed for reproduction at all. Most people believed that inside a bird’s egg or inside a plant’s seed was a preformed, so-tiny-as-to-be-invisible version of the coming creature or, alternatively, its infinitesimal but as yet unassembled parts. Quite likely, it was thought, semen just jump-started its growth.
There was a second part to what became known as the “ovist” theory: Inside the ovary of the infinitesimal hen-to-be are eggs that hold all the future descendants of that unborn hen. In other words, ovists believed that the egg of an animal or the seed of a plant is like a set of Russian nesting dolls. Each new generation is inside the other, ready to emerge into the light at its appointed time. As improbable as the theory sounds to twenty-first-century ears, ovism was actually the most reason-based explanation of reproduction. The only alternative theory was epigenesis, which held that a complete creature came into existence in an egg or a seed out of only the unorganized, raw materials inside. Epigenesis required a supernatural force to operate every day in every act of conception, magically creating a thing out of nothing. To seventeenth-century rationalists this idea was anathema, reeking of medieval occultism. Instead, they held that God intervened in the world only once, when He created the world in six days. When he created living creatures on days five and six, he simultaneously created all their future descendants, lodging them within the wombs, eggs, and seeds of the first generation. Then, having stocked the shelves, He bowed out and left history to unfold.
In 1677, Antonie von Leeuwenhoek added a new explanation of how conception occurs. Leeuwenhoek was a Dutch cloth merchant who made remarkable, simple microscopes. He fashioned his lenses by heating a glass rod in a flame and then pulling the ends apart to draw out a slender glass thread. After breaking the thread, he touched its delicate tip to the flame so it melted and formed an eighth-inch bead, which he painstakingly polished. Finally, he placed the bead in a hol
e in a small brass plate. While its field of vision was very narrow, the magnification was greater than Hooke’s microscope. (I tried a Leeuwenhoek instrument at Notre Dame. It was surprisingly powerful but uncomfortable to use: I had to hold the plate right up to my eyeball and couldn’t blink while looking through it because my lashes would brush the plate.)
Leeuwenhoek was uniquely successful in making this kind of microscope. He was also an unschooled man, spoke and wrote only Dutch, and was paranoid that other, more worldly men like those at the Royal Society would steal his technology. He was happy to share his drawings of his findings with those worthies when they asked, but he never responded to their requests to see his instruments. In 1676, he had sent the first drawings, which were also the first sightings, of single-celled microorganisms, which he called animalcules. The following year, taking up one of his best devices, he peered into a drop of his semen, and a new possibility—or rather millions of new possibilities—for the source of new life wriggled into view: spermatozoa. Leeuwenhoek asserted that inside each of the rounded heads of these new animalcules was a tiny new human waiting to be born. “It is exclusively the male semen that forms the foetus and . . . all that the women may contribute only serves to receive the semen and feed it.” The ovists’ idea of preformed beings was correct, he and other “spermists” opined, but they had the wrong idea about their location. God had put all future human beings not in Eve’s ovaries, but in Adam’s testicles.
The spermist theory quickly won adherents among the natural philosophers. Wasn’t it more likely that the more powerful sex—and the one of which they happened to be members—is the one that creates new life while females simply provide a nest? In 1703, Samuel Morland, an English baronet and a remarkable polymath, applied the spermist theory to the vegetal world, advising that pollen “is a congeries of seminal plants, one of which must be convey’d into every ovum before it can become prolific.”