Читать книгу Molecular Mechanisms of Photosynthesis - Robert E. Blankenship - Страница 40

In the 1640s, a Flemish physician named Jan Baptista van Helmont (1577–1644) planted a willow tree in a tub of earth, which weighed 200 lbs. For five years, he watered the tree and weighed the leaves that fell off each autumn. At the end of that time, he pulled the tree from the tub and weighed both the tree and the tub of earth. The tub of the earth was essentially unchanged in weight, having lost only two ounces, but the tree and its leaves weighed 169 lbs. He concluded that the tree had come from the water that he had given the tree, rather than from the “humus” of the soil, which was the ancient view derived from Aristotle (384–322 BC). Van Helmont's conclusion was only partially correct, as the mass of a plant derives largely from both water and carbon dioxide, the latter of which was completely unknown at the time. However, van Helmont's emphasis on analysis by weighing was considerably ahead of its time, as the law of conservation of matter in chemistry, which is based on a careful weighing of reactants and products of chemical reactions, was not formulated by the French chemist Antoine Lavoisier (1743–1794) for over another 100 years.