[In process.]

Whoever turns to the history of photosynthesis research in the twentieth century is soon confronted with the fact that one of its most exciting periods, the years from 1938 to 1955 (and even beyond), was in large part overshadowed by a bitter controversy in which many of the leading scientists in the field were involved: the dispute on the minimal quantum requirement - or, its inverse: the maximum quantum yield - of photosynthesis. On the one side was Otto H. WARBURG (1883 -1970), who, in 1923, had found that 4-5 light quanta were required for one molecule of oxygen; and who would never accept any other value. On the other side were a number of highly renowned American photosynthesis researchers, among others Robert EMERSON (1903-1959), James FRANCK (1882-1964) and Hans GAFFRON (1902-1979), who contested this value and argued, instead, that 8-12 light quanta were required for one molecule oxygen. This value is still accepted today. In this paper, the course of the controversy is reconstructed on the basis of numerous documents and correspondences that so far have not received much attention. The historically contingent factors will be analyzed that made this controversy so atrocious; however, I will argue that the dispute was not primarily about reputation and glory but in large parts driven by the keen interest of the scientific community to solve a difficult research question - notwiith standing the fact that WARBURG failed to comply with scientific conventions of methodical transparency and mutual.