Law of limiting factor was proposed by $F F$ Blackmann in 1905. He stated that when a process is conditioned as to its rapidity by a number of separate factors, the rate of process is limited by the pace of slowest factor. Blackmanns law of limiting factor is applicable to any physiological process which is affected by more than one factor. von Mayer in $1845$ stated that green plants convert solar energy into chemical energy during the process of photosynthesis. Arnon in $1954$, discovered photophosphorylation. He also showed fixation of $CO_{2}$ by previously illuminated isolated chloroplasts by using radioactive carbon $^{14}C $ in their carbon dioxide. Robin Hill in $1937$ proposed that the evolution of oxygen occurs in light reaction performed by isolated illuminated chloroplast in the presence of suitable electron acceptors and in the absence of $CO_{2}$ .