1. Wald, G. Nature 219, 800–807, (1968).
2. West, W. & Carroll, B. H. in The Theory of the Photographic Process 3rd edn (ed. James, T. H.). 233–277 (Macmillan, New York, 1966).
3. Govindjee in Bioenergetics of Photosynthesis (ed. Govindjee), (Academic, New York, 1975).
4. Burkhardt, D. Symp. Soc. exp. Biol 16, 86–109 (1962).
5. Horridge, G. A. & Mimura, K. Proc. R. Soc. B190, 211–224 (1975).