Augustin de Candolle and Natural Classification
Linnaeus developed the approach to classification that Tournefort had used, but he did not depart from its principles. Under the Linnaean system, plants were grouped together on the basis of similarities in their flowers—the number and arrangement of stamens. His system was easy to learn, so students liked it, but it was unnatural, and in later years much of it had to be dismantled and the groups of species rearranged—requiring former students to painfully unlearn the arrangements they had memorized.
An alternative approach was possible. In 1790 the German poet Johann Wolfgang von Goethe (1749–1832) published Versuch, die Metamorphose der Pflanzen zu eklaren (Attempt to explain the metamorphosis of plants). Goethe believed that the leaf is the basic unit of every plant and that different forms of plants arise through the expansion and contraction of leaves and of organs derived from the modification of leaves. All plant species were, therefore, variations on a single general plan. This idea influenced the Swiss botanist Augustin de Candolle (1778–1841). Candolle was also influenced by the French botanist Antoine-Laurent de Jussieu (1748–1836). In 1788–89, Jussieu, professor of botany at the Jardin des Plantes (1793–1826), published his classification system in his book Genera plantarum (Plant genera). Jussieu had classified plants by first dividing them into three divisions according to whether they had no cotyledons in their embryos (acotyledons), one cotyledon (monocotyledons), or two cotyledons (dicotyledons). He then broke the divisions into 100 families on the basis of other natural features.
Taxonomy was Candolle's passion; indeed, it was he who coined the term in his 1813 book Theorie elementaire de la botanique (Elementary theory of botany), which was the work in which he set out his system of classification—or taxonomy. Candolle based this on the work of Jussieu and the French zoologist Georges Cuvier (1769–1832). Candolle proposed that similarities in the symmetries of their sexual parts revealed whether plants were related, but that these similarities could be obscured by parts fusing together, or degenerating, or by being lost entirely. These modifications could make plants that were truly related appear to be unrelated. To overcome such difficulties, Candolle introduced the concept of homology—the existence in two species of organs or structures that appear different but that are descended from a common ancestor.
Candolle was also the first botanist to recognize that plants compete with each other—he called it being “at war one with another”— for resources. Charles Darwin studied Candolle's plant taxonomy while he was a student at the University of Edinburgh, and the description of plants “at war” was one of the ideas that pushed him toward developing his own evolutionary theory.
Augustin Pyramus de Candolle was born in Geneva, Switzerland, on February 4, 1778. He studied medicine at the Geneva Academy for two years before moving to Paris in 1796, where he added natural sciences to his medical studies. While in Paris, Candolle met many leading scientists, including Georges Cuvier and Jean-Baptiste Lamarck. In 1802 he acted as Cuvier's deputy at the College de France, and he edited the third edition of Flore francaise on behalf of Lamarck. He received his degree of doctor of medicine in 1804 from the University of Paris, but his acquaintance with Cuvier and Lamarck led Candolle to abandon medicine and concentrate wholly on botany. At the request of the French government, he carried out a botanical and agricultural survey of the whole of France. It took him six years, traveling each summer, and the results were published in 1813. In 1808 Candolle left Paris to become professor of botany at the College of Medicine in Montpellier. He left Montpellier in 1816 to become professor of natural history and director of the botanical garden at the Geneva Academy. He remained in these positions until he retired in 1835, when his son Alphonse Louis Pierre Pyramus de Candolle (1806–93) succeeded him and continued his work.
In 1824 Candolle commenced his most important work, Prodromus systematis regni vegetabilis (Introduction to a natural classification of the vegetable kingdom). He intended this 17-volume treatise to cover the taxonomy, ecology, and geography of all known seed plants. By 1839 he had completed seven of the volumes, but then ill health compelled him to abandon work on the project. He died in Geneva on September 9, 1841. Alphonse continued the work, producing the remaining 10 volumes, one of them in collaboration with his own son, Anne Casimir Pyrame de Candolle (1836–1918).
- How Plants Are Classified
- Carolus Linnaeus and the Binomial System
- Joseph Pitton de Tournefort and the Grouping of Plants
- Jose Mutis and the Bogota Botanical Garden
- Jean-Baptiste Lamarck and the Royal Garden, Paris
- Sir William Hooker, the First Official Director
- Sir Joseph Banks, Unofficial Director of Kew
- Sir Henry Capel, Princess Augusta, and the Royal Botanic Gardens at Kew