(1) A method has been developed for studying the
photo-oxidation of plant pigments on thallous bromide;
it depends essentially on the accurate measurement of
the pressure decreases involved, using a sensitive
Bourdon glass-spring gauge.
(2) The results show that, under these conditions,
both freshly prepared and copper-stabilised chlorophyll absorb one molecule of oxygen par molecule of
pigment. This is also true for the carotenoid
fraction. For acid-treated chlorophyll, or phebphytin, this ratio is increased threefold. These oxidations were shown to be partly reversible.
(3) The thallous bromide has been shown to act
merely as a photo-sensitiser.
(4) A thermal oxidation of carotenoids and of
carotenoid/chlorophyll mixtures was observed in the
presence of certain cobalt salts.
(5) It has proved Impossible as yet, with this in
vitro system, to simulate any photosynthetic reaction,
although the effect of carbon dioxide and water
vapour was examined for the majority of the experiments.
(6) A general scheme has been proposed to account
for the main features of the photo-oxidation*