And so we come to life! Now that the compound microscope had been developed, it was possible to examine more minutely the structure of plants, even to the secrets of their sex. Botany graduated from its servitude to medicine, and Linnaeus mapped the teeming world of life with the care and devotion of a scientific saint.
His father, Nils Linné, was pastor of a Lutheran flock at Stenbrohult in Sweden. The son of a clergyman has especial difficulty in preserving his piety, but Carl managed it, and found, especially in the plant world, endless reasons for thankfulness to the Creator. And indeed there are moments when life appears so beautiful that only an ingrate could be an atheist.
Nils was an enthusiastic gardener, who loved to secure choice trees and rare flowers and set them in the soil around his rectory as a living litany of praise. These were Carl’s toys and intimates in boyhood, so that (he tells us) he grew up with “an unquenchable love for plants.”78 Many a day he played truant from school to collect specimens in woods and fields. The father longed to make him a clergyman, for the lad was the soul of goodness, and might teach more by deed than by creed; but Carl took to medicine as the only career in which he could both botanize and eat. So in 1727, aged twenty, he was enrolled as a medical student in the University of Lund. A year later, with glowing recommendations from his teachers, he was sent to the University of Uppsala. As one of five children he could not receive much financial aid from his parents. Too poor to have his shoes repaired, he put paper in them to cover the holes and keep out some of the cold. With such incentives to study, he advanced rapidly in both botany and medicine. In 1731 he was appointed deputy lecturer in botany, and tutor in the home of Professor Rudbeck, who had twenty-four children; “now, through the grace of God,” he wrote, “I have an income.”79
When the Vetenskapssocietet (Scientific Society) of Uppsala decided to send an expedition to study the flora of Lapland, Linnaeus was chosen as leader. He and his young associates set out on May 12, 1732. He described the departure in his naturally flowery style:
The sky was bright and genial; a gentle breeze from the west lent a refreshing coolness to the air.… The buds of the birch trees were beginning to burst into leaf; the foliage on most trees was fairly advanced; only the elm and the ash remained bare. The lark was singing far on high. After a mile or so we came to the entrance of a forest; there the lark left us, but on the crest of the pine the blackbird poured forth his song of love.80
This is typical of Linnaeus; he was ever alert, with every sense, to the sights, sounds, and fragrances of nature, and never admitted any distinction between botany and poetry. He led his troop over 1,440 miles of Lapland, through a hundred dangers and hardships, and brought them back safely to Uppsala on September 10.
Still almost penniless, he tried to support himself by lecturing, but a rival had the lectures prohibited on the ground that Linnaeus had not yet completed the medical course or taken his degree. Meanwhile Carl had fallen in love with “Lisa”—Sarah Elisabeth Moraea, daughter of a local physician. She offered him her savings, he added his own, and, so financed, he set out for Holland (1735). At the University of Harderwijk he passed his examinations and received his medical degree. A year later, at Leiden, he met the great Boerhaave, and almost forgot Lisa. Inspired and helped by that nobleman of science, Linnaeus issued one of the classics of botany, Systema Naturae. It ran through twelve editions in his lifetime; in the first it consisted of only fourteen folio sheets; in the twelfth it ran to 2,300 pages, in three volumes octavo. Near Amsterdam he replenished his funds by reorganizing and cataloguing the botanical collection of George Cliffort, a director of the East India Company. With incredible industry he brought out in 1736Bibilotheca botanica, and in 1737 Genera Plantarum. In 1738 he went to Paris to study the Jardin du Roi. There, without introducing himself, he joined a group of students to whom Bernard de Jussieu was lecturing in Latin on exotic plants. One plant puzzled the professor; Linnaeus ventured to suggest, “Haec planta faciem americanam habet” (This plant has an American appearance). Jussieu looked at him, and surmised, “You are Linnaeus.” Carl confessed, and Jussieu, with the fine brotherhood of science, gave him an unstinted welcome.81 Linnaeus was offered professorships in Paris, Leiden, and Göttingen, but he thought it time to return to Lisa (1739). Such long betrothals were not then unusual, and in many cases they probably contributed to stability of morals and maturity of character. They married, and Carl settled down as a physician in Stockholm.
For a time, like any young doctor, he waited in vain for patients. One day in a tavern he heard a youth complain that no one had been able to cure him of gonorrhea. Linnaeus cured him, and soon other young men who had been too anxious to prove their manhood came for similar relief. The doctor’s practice spread to lung ailments. Count Carl Gustav Tessin, speaker of the House of Nobles in the Riksdag, became acquainted with him, and secured him appointment as physician to the Admiralty (1739). In that year Linnaeus helped to found the Royal Academy of Science, and became its first president. In the fall of 1741 he was chosen professor of anatomy at Uppsala; soon he exchanged this chair for that of botany, materia medica, and “natural history” (geology and biology); at last he was the right man in the right place. He communicated his enthusiasm for botany to his students; he worked with them in informal intimacy, and he was never so happy as when he led them on some natural-history foray.
We made frequent excursions in search of plants, insects, and birds. On Wednesday and Saturday of each week we herborized from dawn till dark. Then the pupils returned to town wearing flowers in their hats, and escorted their professor to his garden, preceded by rustic musicians. That was the last degree of magnificence in our pleasant science.82
He sent some of his students to various quarters of the world to secure exotic plants; for these young explorers (some of whom sacrificed their lives in their quest) he secured free passage on the ships of the Dutch East India Company. He stimulated them with the hope of adding their names to plants in the great system of nomenclature that he was preparing. They noted that he gave the name camellia to the flowering shrub that had been found in the Philippines by the Jesuit George Kamel.
In the Systema naturae, the Genera Plantarum, the Classes Plantarum (1738), the Philosophia botanica (1751), and the Species Plantarum (1753) he built up his monumental classification. In this task he had several predecessors, especially Bauhin and Tournefort; and Rivinus had already (1690) suggested a binomial method of naming plants. Despite these labors Linnaeus found the collections of his time in a state of disorder that seriously hampered the scientific study of plants. Hundreds of new varieties had been discovered, to which botanists had given conflicting names. Linnaeus undertook to classify all known plants first by their class, then in the class by their order, in the order by their genus, in the genus by their species; so he arrived at a Latin name internationally acceptable. As the basis of his classification he took the presence and character, or the absence, of distinctively reproductive organs; so he divided plants into “phanerogams,” those having visible organs of reproduction (their flowers), and “cryptogams,” in which (as in mosses and ferns) there are no flowers producing seeds, and the reproductive structures are hidden or inconspicuous.
Some timid souls objected that this emphasis on sex would dangerously influence the imagination of youth.83 Hardier critics, in the course of the next hundred years, pointed out more basic defects in Linnaeus’ classification. He was so interested in finding nooks and names for plants that for a time he diverted botany from the study of plant functions and forms. Since a transformation of species would have confused his system, and would have contradicted the Book of Genesis, he laid down the principle that all species had been directly created by God and had remained unchanged throughout their history. Later (1762) he modified this orthodox attitude by suggesting that new species might arise by the hybrid crossing of kindred types.84 Though he treated man (whom he trustfully called “homo sapiens”) as part of the animal kingdom, and classified him as a species in the order of primates, along with the ape, his system impeded the development of evolutionary ideas.
Buffon criticized the Linnaean classification on the ground that genera and species are not objective things but are merely names for convenient mental divisions of a complex reality in which all classes, at their edges, melt into one another; nothing exists, outside the mind, except individuals; here was the old medieval debate between realism and nominalism. Linnaeus (proving himself human) replied that Buffon’s eloquence must not be allowed to deceive the world; and he refused to eat in a room where Buffon’s portrait was hung along with his own.85 In a more genial moment he admitted that his arrangement was imperfect, that classification of plants by sexual apparatus left many loose ends; and in Philosophia botanica he proposed a “natural” system based upon the form and development of the organs of a plant. His nomenclature, as distinct from his classification, proved to be a great convenience, both in botany and in zoology, and with some modifications it still prevails.
In his old age Linnaeus was honored by all Europe as the prince of botanists. In 1761 he was knighted by the King, and became Carl von Linné. Ten years later he received a love letter from the second most famous author of the century, Jean Jacques Rousseau, who had translated the Philosophia botanica, and had found in botanizing a cure for philosophy: “Accept, kind sir, the homage of a very ignorant but very zealous disciple of yours, who owes in great part to meditation on your writings the tranquillity he enjoys… I honor you, and I love you with all my heart.”86
Linnaeus, like Rousseau and Voltaire, died in 1778. His library and botanical collections were bought from his widow by James Edward Smith, who joined others (1788) in founding the Linnaean Society of London to care for the “Linnaean treasure.” From that center a long series of publications spread the work of the botanist throughout Europe and America. Goethe named, as the greatest influences in his mental life, Shakespeare, Spinoza, and Linnaeus.87
2. In the Vineyard
Hundreds of devotees carried on the botanic quest. In France we find one of those virile families where a common dedication unites the members across the centuries. Antoine de Jussieu, coming up to Paris from Lyons, rose in 1708 to be director of the Jardin du Roi. His younger brother Bernard was a lecturer and “demonstrator” there; we have seen him welcoming Linnaeus. Another brother, Joseph, went to South America with La Condamine, and sent the Heliotropium peruvianum for transplantation in Europe. A nephew, Antoine Laurent de Jussieu, published in 1789 the work that began to replace the Linnaean system: Genera plantarum secundum ordines naturales disposita. He classified plants morphologically (according to their forms) by the presence, absence, or number of cotyledons (seed leaves): those plants that had none he called acotyledons; those with one only, monocotyledons; those with two, dicotyledons. His son Adrien carried on their work into the nineteenth century. In 1824 Augustin de Candolle, building upon the labors of the Jussieus, outlined the classification that is received today.
The sexuality of plants had been discovered by Nehemiah Grew in or before 1682, and had been confirmed by Camerarius in 1691. Cotton Mather reported from Boston to the Royal Society of London (1716) a demonstration of hybridization by wind pollination:
My neighbor planted a row of hills in his field with our Indian corn, but such a grain as was colored red and blue; the rest of the field he planted with corn of the most usual color, which is yellow. To the most windward side this row infected four of the next neighboring rows, … to render them colored like what grew on itself. But on the leeward side no less than seven or eight rows were so colored, and some smaller impression was made on those that were yet further distant.88
In 1717 Richard Bradley proved the necessity of fertilization by an experiment with tulips. From twelve of these, “in perfect health,” he removed all pollen; “these bore no seed all that summer, while … every one of four hundred plants which I had let alone produced seed.”89 He studied cross-fertilization, and foresaw some fascinating results. “By this knowledge we may alter the property and taste of any fruit by impregnating the one with the farina [pollen] of another of the same class” but of a different variety or species. Moreover, “a curious person may by this knowledge produce such rare kinds of plants as have not yet been heard of”; and he told how Thomas Fairchild had grown a new variety “from the seed of a carnation that had been impregnated by the farina of the sweet William.” He found such interspecies hybrids to be sterile, and compared them with mules.
Philip Miller, in 1721, gave the first known account of plant fertilization by bees. He removed the “apices” of certain flowers before they could “cast their dust”; yet the seed of these apparently emasculated flowers ripened normally. Friends questioned his report; he repeated the same experiment more carefully, with the same result.
About two days after, as I was sitting in my garden, I perceived in a bed of tulips near me some bees very busy in the middle of the flowers; on viewing them I saw them come out with their legs and bellies loaded with dust, and one of them flew into a tulip that I had castrated; upon which I took my microscope, and examined the tulip he flew into, and found he had left dust enough to impregnate the tulip; which, when I told my friends, … reconciled them again.… Unless there be provision to keep out insects, plants may be impregnated by insects much smaller than bees.90
Josef Kölreuter, professor of natural history at Karlsruhe, made a special study (1760 f.) of cross-fertilization and the physiochemistry of pollination. His sixty-five experiments had immense influence on agriculture in several continents. He concluded that crossing is fruitful only in closely related plants; but when it is successful the hybrids grow more rapidly, flower sooner, last longer, and produce young shoots more abundantly than the original varieties, and are not weakened by developing seed. Konrad Sprengel showed (1793) that cross-fertilization—usually by insects, less often by wind—is common within a species; and he argued, with warm teleological conviction, that the form and arrangement of parts in many flowers is designed to prevent self-fertilization. Johann Hedwig opened up a new field of research by studying the reproductive process in cryptogams (1782). Between 1788 and 1791 Joseph Gärtner of Württemberg issued, in two installments, his encyclopedic survey of the fruit and seeds of plants; this became the groundwork of nineteenth-century botany.
In 1759 Caspar Friedrich Wolff, in his Theoria Generationis, enunciated a theory of plant development usually ascribed to Goethe:
In the entire plant, whose parts we wonder at as being at first glance so extraordinarily diverse, I finally perceive and recognize nothing beyond leaves and stem, for the root may be regarded as a stem.… All parts of the plant, except the stem, are modified leaves.91
Meanwhile a major figure in eighteenth-century science, Stephen Hales, explored the mystery of plant nutrition. He was another of those many Anglican clergymen who found no hindrance in their flexible theology to the pursuit of science or scholarship. Though accepting divine design, he made no use of this in his scientific inquiries. In 1727 he published his results in one of the classics of botany, Vegetable Staticks, … an Essay towards a Natural History of Vegetation. His preface explained:
About twenty years since, I made several haemostatical experiments on dogs, and six years afterwards repeated the same on horses and other animals, in order to find out the force of the blood in the arteries [our “systolic blood pressure”].… At which time I wished I could have made the like experiments to discover the force of the sap in vegetables; but despaired of ever effecting it till, about seven years since, I hit upon it while I was endeavoring by several ways to stop the bleeding of an old stem of a vine.92
Harvey’s discovery of the circulation of the blood in animals had led botanists to assume a similar circulatory movement of liquids in plants. Hales disproved this supposition by experiments that showed a tree absorbing water at its branches’ ends as well as by its roots; water moved inward from branches to trunk as well as from trunk to branches; and he was able to measure the absorption. Sap, however, moved up from roots to leaves through the pressure of sap expanding in the roots. The leaves absorbed nourishment from the air.
At this point the ingenious Priestley illuminated the problem by one of the most brilliant discoveries of the century—the nutritive absorption, by the chlorophyll of plants in sunlight, of carbon dioxide exhaled by animals. He described this part of his work in the first volume (1774) of his Experiments and Observations:
I took a quantity of air, made thoroughly noxious by mice breathing and dying in it, and divided it into two parts; one of which I put into a phial immersed in water; and in the other [which was] contained in a glass jar standing in water, I put a sprig of mint. This was about the beginning of August, 1771, and after eight or nine days I found that a mouse lived perfectly well in that part of the air in which the sprig of mint had grown, but died the moment it was put into the other part of the same original quantity of air, and which I had kept in the very same exposure, but without any plant growing in it.
After several similar experiments Priestley concluded that
the injury which is continually done to the atmosphere by the respiration of such a number of animals, and the putrefaction of such masses of both vegetable and animal matter, is in part at least repaired by the vegetable creation. And notwithstanding the prodigious mass of air that is corrupted daily by the abovementioned causes, yet, if we consider the immense profusion of vegetables upon the face of the earth, … it can hardly be thought but that it may be a sufficient counterbalance to it, and that the remedy is adequate to the evil.93
In 1764 the Dutch biologist Jan Ingenhousz, domiciled in London, became acquainted with Priestley. He was impressed by the theory that plants purified the air by absorbing, and thriving on, the carbon dioxide exhaled by animals. But Ingenhousz found that plants do not perform this function in the dark. In Experiments on Vegetables (1779) he showed that plants as well as animals exhale carbon dioxide, and that their green leaves and shoots absorb this, and exhale oxygen, only in clear daylight. So we remove flowers from hospital rooms at night.
The light of the sun, and not the warmth, is the chief reason, if not the only one, which makes the plants yield their dephlogisticated air [i.e., oxygen].… A plant … not capable … of going in search of its food must find, within … the space it occupies, everything which is wanted for itself.… The tree spreads through the air those numberless fans, disposing them … to incumber each other as little as possible in pumping from the surrounding air all that they can absorb from it, and to present … this substance … to the direct rays of the sun, on purpose to receive the benefit which that great luminary can give it.94
This, of course, was only a partial picture of plant nutrition. Jean Senebier, a Geneva pastor, showed (1800) that only the green parts of plants are able to decompose the carbon dioxide of the air into carbon and oxygen. In 1804 Nicolas Théodore de Saussure, son of the Alpine explorer, studied the contribution of the soil, in water and salts, to the nourishment of plants. All these studies had vital results in the epochal development of soil fertility and agricultural production in the nineteenth and twentieth centuries. Here the vision and patience of scientists enriched the table of almost every family in Christendom.