In "Recherches chimiques sur la Végétation", Saussure showed that the increase in the mass of a plant as it grows could not be due only to the uptake of CO2, but was also a result of the incorporation of water into plant dry matter. In addition, Saussure demonstrated that plants obtain their carbon from the carbon dioxide in the atmosphere, not through uptake from humus in the soil, as his immediate predecessors in photosynthesis research had generally believed. He also showed that plants require mineral nutrients, which they take up from the soil, and nitrogen, although he did not trace the source of plant nitrogen definitively to the soil. Saussure's finding that the source of plant minerals was the soil disproved the widely held view that mineral substances in plants arose from vague "transmutations" within the plant. His work enabled completion of the basic, overall chemical equation of photosynthesis, according to which carbon dioxide and water, in the presence of light, are converted by a green plant into fixed carbon (such as glucose, food for the plant), with gaseous oxygen released as a byproduct. Based on his accomplishments in plant chemistry and physiology, Saussure is considered the last of the major early pioneers of photosynthesis research, completing the work begun by his predecessors, including Jan Baptist van Helmont, Joseph Priestley, Jan Ingenhousz, and Jean Senebier.