by Christoffer Basse Eriksen
As Charles Darwin was vacationing in the Bournemouth area in the autumn of 1862, he noticed an unfamiliar phenomenon. During his leisurely strolls around the clover fields that surrounded the cottage in which he and his family stayed, he observed how a certain kind of hive bee employed two different strategies to reach the nectar of the red clover flowers. Some, Darwin wrote, “rout about” in the head of the flower, as most bees do, while others bite through the corollas at the base of the flower to get to the nectar from the side. He wrote to his friend John Lubbock to ask for assistance in corroborating his hypothesis that these bees consisted of two different castes with, respectively, long and short proboscises. This never happened, though, for the next day Darwin sent a follow-up letter stating that his observation of the corolla-biting hive bee had been an embarrassing error: “I hate myself[,] I hate clover & I hate bees,” he wrote rather self-deprecatingly.
Darwin observed neither insects nor flowers, but rather insects-and-flowers, understood as intimately linked. In his book on British orchids, published just half a year prior, he had shown how certain insects, including bees, morphologically fit certain orchids. A bee’s long proboscis allows it to reach nectar deep inside the orchid flower and, inversely, the nectar’s depth demands that the bee make sufficient contact with the orchid’s pollen-rich interior to pollinate the next orchid that it reaches. Darwin used such observations to build a convincing argument for his theory of “co-evolution,” the reciprocal evolution of species. While he may have been wrong about the corolla-biting hive bees of Bournemouth, Darwin’s observations of insects-and-flowers marked a defining moment in the history of ecology, as Darwin understood flowers as dependent upon their immediate environment rather than as self-sustaining entities. If we consider ecology as a set of theories about earth’s fabric of life, Darwin stands firmly at the beginning of a tradition. Since Darwin, biologists have studied different kinds of ecological relationships—whether mutualistic, parasitic, or symbiotic—in detail, and ecology has developed into an important subdiscipline of biology.
But focusing on Darwin’s observational style reveals a longer history of flowers, bees, and the observer. Here, Darwin appears as the heir to a longer tradition in botany and gardening, which culminated in the systematic study of plant-animal entanglements in the eighteenth century. By the seventeenth century, European botanists and gardeners observed plant-animal interactions with regularity, if not systematic or causal clarity. Maria Sibylla Merian’s beautiful images of flowers and insects suggest relationships linking pineapples, pomegranates and bananas to moths, butterflies and bees. Beekeepers’ manuals of the period instructed gardeners to place beehives near certain kinds of trees and flowers to increase honey yields. Similarly, the great natural historian Sir Thomas Browne argued in his Garden of Cyrus that each species of plants produces its own species of insects, as if the clover flower produced the bumblebee. While Browne may have inverted the causal relationship, he and Merian took important steps towards the formulation of a flower ecology and a recognition that plants depend on living beings in their shared environment in addition to elemental factors like heat, water and sunlight. Throughout the eighteenth century, a number of botanists and gardeners investigated this causal relationship, seeking to specify the mutual dependency between bees and flowers with increasing systematicity. While we often associate ecology with the idea of a free and unrestrained nature, this history reminds us that the ecological vision of nature had its origin within the highly controlled environments of elite European gardens.
Studying early ecological observational styles also contributes to mounting challenges to an established historiography from the likes of François Jacob and Michel Foucault, which posited classification as the Enlightenment’s ruling spirit and taxonomy as its manifestation. That frame took Carolus Linnaeus’s observations as exemplary of Enlightenment natural history: each species fixed on its own page in the book of nature without any necessary relation to the one beside it. A flower with one stamen belonged to his class of Monandria and a flower with two stamens to Diandria, with the number of pistils specifying each flower’s order. For Linnaeus, observations of stamens and pistils revealed an essential quality of the flower in and of itself. Yet recent scholarship on Linnaeus, points out that, while his principles for identification and naming deliberately excluded much information about plants’ surroundings, his natural-philosophical dissertations, such as On the Use of Natural History or A Dissertation on the Sexes of Plants, demonstrate a high degree of sensitivity towards the importance of the shared space of plant communities within the “economy of nature.”
More broadly, environmental historians and historians of political ecology remind us that eighteenth-century agrarian economies placed the utmost importance on plants’ reproductive cycles. As a result, investigations of the growth of forests, fields, plantations and gardens included observations and experiments on the natural surroundings of plants, including the air, water, earth, but also living neighbours such as other plants and animals. In mid-eighteenth century France, for example, the naturalist Henri-Louis Duhamel du Monceau mobilized amateur entomologists to collect information about the caterpillars that raged the fields of the country, so that he could study their generation and make suggestions for new forms of pest control. For du Monceau and likeminded entomologists, the lifecycles of plants and insects were indeed intertwined, though not in a mutually supportive way, as insects caused the degeneration of plants. However, other naturalists in the same period came to see insect activity as beneficial to the generation of plants—as pollinators rather than as pests. This fostered another conception of the stamens and pistils of flowers. Rather than being keys to universal classification, they were considered functional elements within an open environment that transferred pollen in a variety of ways, including through the movement of insects.
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In the summer of 1721, an involuntary castration took place in the Chelsea Physic Garden. Armed with forceps and a small pair of scissors, the chief gardener Philip Miller carefully grasped the pistil of a tulip in the process of blooming and cut it off, then repeated this irrevocable action until he had rendered the entire bed of tulips infertile. Or had he? As the summer progressed, Miller observed that bees loaded with pollen from the garden’s many other flowerbeds of tulips buzzed around in the castrated tulips, where they deposited some of their flower dust. Much later in the season, Miller established that the castrated tulips had in fact produced fertile seeds. Miller thus concluded that, at least in this case, honeybees could play a vital role in the reproductive cycle of plants.
Miller had not set out to establish the importance of bees to pollination. Rather, he had designed the tulip experiment as part of a larger investigation of the claim made by the plant anatomist Nehemiah Grewa couple of decades prior that plants, like animals, are gendered beings. Shortly after the Dutch microscopist Antoni van Leeuwenhoek identified the sperm cell with microscopes, his English Royal Society colleague Grew used this observation to establish pollen as the vegetable counterpart to the animal sperm. According to Grew, pollen set the reproductive cycle in motion, but he left the exact mechanisms of this cycle unclear. In the 1720s, Miller collaborated with natural historians Richard Bradley and Patrick Blair to investigate the finer details of Grew’s theory: by which means did the transfer of pollen take place? Did it make a difference if the pollen comes from the same flower, from another flower on the same plant, or from another plant entirely? And what force within pollen made it necessary for the production of fertile seeds? To answer these questions, Miller, Bradley and Blair dissected both flowers and bees and conducted versions of the tulip experiment with small variations. This did not lead to any kind of agreement about the respective roles of flowers and bees in plant reproduction, though. In his treatises, Bradley argued that it was absolutely necessary that the “eggs” within the “uterus” of the female pistil were impregnated with the “Male Seed of the same Plant, or one of the same sort.” Blair, on the other hand, argued tenaciously that there was no need for the male dust to enter the insides of the female organs, and that in fact they were not able to, because the female “vasculum seminale,” or uterus, did not have a passageway large enough for them to enter. However, this didn’t disprove gendered reproduction, because, as Blair saw it, the function of the male dust was simply to act as “a more subtile, active Principle, to quicken, enliven, and dispose this gross Substance of the Seed to Fertility.” As such, Blair was in even greater agreement with Nehemiah Grew, who also argued that the male dust only imbued the female seed with a “prolifick virtue,” which worked like a spark to set the development of the seed in motion.
Disagreeing with Blair’s spiritual understanding of generation, Bradley replied in a short treatise that Blair had observed the pistil of the flower at the wrong time and in the wrong situation: just as the female animal’s reproductive organs were more relaxed “in coitu,” during the sexual act, the petals of the flower opened when the sun shined brightly on them, which then relaxed the female parts, preparing them to receive the male dust. Note here that, in the sexual relationship of the animal world, generation was strictly an affair between two beings of the same species. Plants, though, cannot move, and so the sun acted as a third partner in the act, so to speak, preparing them for fertilisation. Miller’s conclusion that the bees played a role as distributors of pollen was merely tangential to his research program, and yet, as the eighteenth century progressed, natural-historical interest shifted from the reproduction of plants in isolation towards an exploration of insect pollination and interspecies relationships between plants and insects.
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The first systematic attempt to investigate the role of insects in cross-fertilization took place in a little garden in Karlsruhe, where the young professor of botany Joseph Gottlieb Kölreuter carried out a series of plant breeding experiments on tobacco plants. Kölreuter wanted to show that it was possible to create fertile hybrids through controlled crossbreeding. Importantly, Kölreuter recognized the potential threat posed to the purity of his crossbreeds by the activity of their ambient surroundings, including perhaps insects. To test the role played by insects in reproduction, Kölreuter carried out a series of painstaking observations on artificially fertilized plants. Using a small camel-hair brush, Kölreuter manually transferred pollen from one tobacco plant to another, after which he spent night and day protecting these plants from insect visits. He did so in different ways: covering the plants in insect nets, placing them in insect-free greenhouses, or simply sitting guard by the plants to manually battle away the disturbing insects for hours on end. When these tobacco flowers ceased blooming, he counted how many seeds they produced, compared their output with tobacco flowers left untouched in his garden, and concluded that the haphazard motion of insects produced more seeds than his own meticulous brushing. This result sparked religious awe in Kölreuter: no matter how much systematic labour he invested, the free work of God’s tiniest beings proved to be far superior. Kölreuter recognized the significance of insects’ role in the fertilization of tobacco plants, albeit in an inverted sense, as it underscored the necessity of maintaining the isolation of his artificially crossbred plants.
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Through their experiments on tulip and tobacco flowers, Miller and Kölreuter recognised that the immediate environment—including the presence of insects within this environment—played a crucial role in plant reproduction. Yet they did not consider that the relationship between flowers and insects is not only general, but also particular, bonding specific kinds of flowers with their corresponding insect pollinators. This changed in the lateeighteenth century through the observations of German naturalist Christian Konrad Sprengel, as published in Das entdeckte Geheimnis der Natur im Bau und in der Befruchtung der Blumen [The Secret of Nature Revealed in the Form and Fertilization of Flowers] in 1793. Sprengel had studied with the botanist Carl Ludwig Willdenow and was making a living as rector of a high school in Spandau, just outside of Berlin. Willdenow had published his catalogue of Berlin’s flowers, the Florae Berolinensis prodromus, in 1787, and had encouraged Sprengel to carry out a similar survey in the local meadows and woods of Spandau. But whereas Willdenow’s catalogue followed the by-then established genre conventions for describing local flora, Sprengel not only enumerated the species found in his local environment, but also compared his detailed observations of the intimate anatomy of each described flower species, including their stamens and pistils, with the insect species that he found visiting them. In his book’s introduction, he describes how he would sit still in the proximity of certain flowers for several hours to observe which species of bees, moths, hoverflies and other insects would visit them, rather than to chase them away, as Kölreuter did. These observations convinced him that each flower species was pollinated by insect species with which they shared morphological traits, including size, shape and colour. Like Kölreuter, this led Sprengel to praise the astounding fine-tuning of the different parts of God’s nature: “That these and other insects, while pursuing their food in the flowers, at the same time fertilize them without intending and knowing it and thereby lay the foundation for their own and their offspring’s future preservation, appears to me to be one of the most admirable arrangements of nature,” he wrote. In a series of copper etchings at the end of the book, Sprengel presented this shared anatomy in a striking, visual form: curled up in the flowers to the point of being almost unnoticeable, one finds bees and bumblebees caught in the act of sucking up the nectar, delivering pollen in the process (see cover image).
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The image of the bee buzzing from flower to flower, sustaining itself on nectar while furthering plant reproduction by distributing pollen, has become a core representation of ecological relations. But it was only through the epistemic work of range of eighteenth-century botanists that bees emerged as pollinators within this mutually beneficial relationship. The history of the discovery of insect pollination lays bare a fundamental tension within the history of ecological thought: though knowledge of cross-species entanglement generates admiration for non-human nature and a desire to protect it, it also fosters new attempts to manipulate this entangled nature to further human-consumable commodity production.
While we should not equate ideas formulated across different contexts, these eighteenth-century observations of the interwoven nature of flowers and bees conditioned much later awareness of the need to protect and preserve biodiversity. Both Kölreuter and Sprengel used a rich theological vocabulary to extoll the intricacies of nature, as they observed how different kinds of natural beings seemed to be woven into each other through shared morphological and functional traits. Through their observational setups and new ideas about the importance of pollen transfer, they were able to see what no one had seen before, namely the invisible relations connecting the life cycles of flowers and insects, and Kölreuter was quite clear that these functions could not be perfectly replicated by human action—pollination by his camel-hair brush was inferior to the free movement of buzzing insects.
At the same time, this history also reveals the depth of insect pollination’s ingraining in the history of agricultural optimization. As we have seen, Miller conducted his pollination experiments within the Chelsea Physic Garden, one of the most prolific botanical gardens of the time. Among other things, Miller’s garden functioned as a halfway house in which plants from the colonies were adapted to the English environment. Figuring out the mechanisms of plant reproduction—including the importance of insect activity—was an integral part of such efforts to make colonial plants proliferate in new climates. This ambition is found in Sprengel’s statement in the introduction to Das Entdeckte Geheimnis that his observations on the anatomy of flowers and insects would shed light on difficulties with facilitating flower reproduction in greenhouses, which likewise concerned Kölreuter. Darwin, too, was preoccupied with optimizing agricultural production in his experiments on the fertilization of legumes, especially white and red clover, which concluded that the presence of active bees near the fields increased the crop yield considerably, a practice still in use today.
To eighteenth-century observers, these two elements coexisted; the history of the discovery of insect pollination is a story of growing ecological awareness as much as it is a story of increased management of nature. Today, both elements are mobilized in parallel attempts to protect biodiversity through insect-friendly environments and the use of insect-pollinators to facilitate the cultivation of non-native crops in greenhouses. This is a forceful reminder that even the images of nature seemingly most distant from any human interference—such as the ostensibly free activity of insects in a flower patch—carry traces of their cultural installation.
Christoffer Basse Eriksen is a postdoctoral fellow at the Centre for Science Studies, Aarhus University. He completed his PhD in history of ideas from Aarhus University in 2018 followed by research positions at University of Cambridge and Humboldt-Universität of Berlin. He is currently investigating the making of the Danish multi-volume botanical atlas Flora Danica and has published widely on early modern microscopy in journals such as British Journal for the History of Science, Centaurus, and History of Science. He was recently awarded the Margaret W. Rossiter History of Women in Science Prize by the History of Science Society.
Edited by Zac Endter
Cover image: Christian Konrad Sprengel, Das entdeckte Geheimnis der Natur im Bau und in der Befruchtung der Blumen (Berlin: Friedrich Vieweg, 1793), Tab. XXIII. Image taken from Charles Darwin’s private copy. Courtesy of Cambridge University Library.
