In 1727, Stephen Hales suggested that plants take nutrients from the air with the help of leaves. In 1905, Blackman divided the photosynthesis process into light and dark stages. In 1931, scientist Van Niel discovered the similarity between photosynthesis in green plants and bacteria. In 1937, scientist Robin Hill proved that water is the source of O2 released in the process of photosynthesis. In 1941 Ruben, Kamen and Randall proved the source of O2 using isotopes. Calvin, Basham and Benson discovered the C3 cycle in 1954. Hatch and Slack discovered the C4 cycle in 1966.