hill reactions occur in

1. high altidute plants
2. total darkness
3. absence of water
4. presence of ferricyanide

Further experiments to prove that the oxygen developed during the photosynthesis of green plants came from water, were performed by Hill in 1937 and 1939. He showed that isolatedchloroplastsgive off oxygen in the presence of unnatural reducing agents like ironoxalate,ferricyanideorbenzoquinoneafter exposure to light. The Hill reaction.