Jan Baptist Van Helmont (1580-1644), the Flemish physician and chemist, was the first person to demonstrate that soil contributes very little to the increase in the weight of plants. The Greeks believed that plants derived their nourishment from the soil only.
He was also the first to postulate the existence of gases distinct from air. He believed that the prime elements of the universe were air and water. This brilliant Belgian scientist showed that plants are composed only of water by planting a willow of known weight in soil of known weight and weighing the willow and the soil five years later.
The willow had gained 76.7 kg (169 lb) and the soil had lost practically no weight. He ascribed the gain in weight of the willow to its having taken up water. For the modern explanation of his experiment, please look up details on photosynthesis. His works were published posthumously in 1648 as Ortus Medicinae.