Ingenhousz

Jan Ingenhousz (1730–1799) was a Dutch physician, chemist, and biologist whose research on plant physiology laid the foundation for modern understanding of photosynthesis. Born in the town of Breda in the Dutch Republic, Ingenhousz studied medicine at Leiden University, receiving his doctorate in 1755. After completing his medical training, he practiced as a physician in several Dutch cities, including Amsterdam and Utrecht, while pursuing scientific investigations in his spare time.

In 1779, Ingenhousz published the seminal work Experiments on Vegetables, in which he demonstrated that green plants release a gas that supports combustion and animal respiration only in the presence of light. Building on the earlier discovery of oxygen by Joseph Priestley, Ingenhousz showed that this “vital air” was absorbed during daylight and emitted at night, thereby establishing the reversible nature of the process now known as photosynthesis. His experiments also confirmed that the effect was confined to the green parts of plants and that non‑green tissues did not exhibit the same activity.

Ingenhousz’s findings earned him membership in several scientific societies, including the Royal Society of London, which awarded him the Copley Medal in 1785. He continued to work in both medicine and natural philosophy, publishing papers on topics such as animal respiration, the composition of gases, and the chemistry of blood. He died in Amsterdam in 1799, leaving a legacy that influenced subsequent generations of botanists and chemists, and cementing his place as a key figure in the history of plant science.