Professor M. Calvin of the University of California in the United States, along with his two colleagues Bessham and Benson Benson, described the process of carbon assimilation in the light neutral stage of photosynthesis, called the Calvin-Besham cycle. The first stable compound produced in this cycle is the three-carbon 3-phosphoglyceric acid and is called the C3 cycle. They discovered this cycle in Chlorella and Scenedesmas algae in 1947 using radioactive carbon (14C) (Tracer method). They won the Nobel Prize in Medicine and Physiology in 1961 for their discovery.