Jan Ingenhousz (1730 - 1799), a Dutch physician and plant physiologist, confirmed in 1779 that in sunlight, plants absorb carbon dioxide and give off oxygen. Ingenhousz's work, published in Experiments On Vegetables, Discovering their Great Power of Purifying the Common Air in Sunshine, and of Injuring it in the Shade or at Night, laid the foundations for the study of photosynthesis. This was the first indication of light's role in the photosynthetic process. Ingenhousz also discovered that only the light of the Sun—and not the heat it generates—is necessary for photosynthesis. He found that plants, like animals, respire all the time and that respiration occurs in all the parts of plants. He further concluded that plants were converting carbon dioxide into oxygen, which animals converted back into carbon dioxide. Ingenhousz also showed that only the green parts of plants carry out photosynthesis. For elucidating these processes, Ingenhousz is considered among the discoverers of photosynthesis.

Further Reading
Chemistry of Life: Jan Ingenhousz (Chemical Heritage Foundation)