Sparking a Fever for Botanical Knowledge
Mimosa pudica. Image via Wikimedia Commons
From Lapham’s Quarterly:
Sometime around the late eighteenth century, the French botanist René-Louiche Desfontaines took a plant on an outing around Paris in a horse-drawn carriage. At the time, botany was just emerging as an independent science separate from medicine and herbalism. Desfontaines, who’d been elected to the Académie des Sciences at the age of thirty-three and appointed professor of botany at the Jardin des Plantes a few years later, was a leading practitioner in the new field. Only a few decades before, Carl Linnaeus had sparked a fever for botanical knowledge with his revolutionary approach to classifying and naming species. The Linnaean system offered a rational way to understand nature and creation, and the educated elite readily embraced it. Up to five hundred Parisian botanophiles (as the new plant lovers were called) regularly turned out for Desfontaines’ thrice-weekly lectures at the Jardin, eager to learn more about his plant-collecting adventures in North Africa and the new species he’d carried home and was busy describing. Perhaps he told his audiences about his carriage experiment; it would have fit with botanists’ realization that plant sex was analogous to animal sex, something many laypeople found profoundly shocking. As it stands, Desfontaines left only a brief mention of this excursion in an obscure volume he wrote about the nature of French trees and shrubs.
From this account, we know that the plant he selected for the tour was one most of us call the sensitive plant or touch-me-not, Mimosa pudica. A member of the pea family, M. pudica is a small plant with tiny leaflets paired along the length of each stem and pretty lavender-pink globular flowers. The leaves give it a fernlike, feminine look, although it is also armed with thorns to ward off attacks. It’s native to Central and South America but has spread throughout the tropics partly because of its popularity as a novel ornamental that exhibits a fascinating behavior: if you touch a single leaf, the plant will swiftly fold up all its leaves before your eyes. Only a soft touch is required to bring on this collapse; after a while, you can also watch as the wilted-appearing mimosa sets about righting itself and reopening its leaves. You may have discovered the mimosa’s animal-like trick in an arboretum or store where the plants are sometimes displayed or sold. The rapid response to being touched is another defensive tactic—it startles most insects, as it does naive humans.
M. pudica and its curious actions were known to Western science even before 1753, when Linnaeus officially named the species. Many leading scientists of the day, including Robert Hooke (the English natural philosopher best known for being the first to see and describe a cell via a microscope) and later the French naturalist Jean-Baptiste Lamarck studied the plant. Lamarck was particularly struck by how mimosas eventually no longer respond to being repeatedly touched. He thought this was likely due to the plant running out of energy. But sometimes they stopped responding long before they depleted their stores. He couldn’t explain why they stopped until he learned of Desfontaines’ carriage experiment.