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Abstract. Action spectra were obtained for photosystems I and II in chemically fixed algal cells and for photosystem I in unfixed lysozyme treated cells. Untreated algal cells yielded neither of the 2 light reactions with the reaction mixtures used. The action spectra for photosystem I in the blue-green alga Anacystis nidulans and red alga Porphyridium cruentum follow the absorption spectrum of chlorophyll a with a small peak in -the region of the accesisory pigments. In the green alga Chlorella pyrenoidosa the photosystem I action spectrum follows the absorption spectrum of chlorophyll a. Photosystem II action speotra in A. nidulans and P. cruentum follow the absorption spectra of the accessory pigments while that in C. pyrenoidosa is shifted slightly toward the blue spectral region. These results provide additional evidence that formaldehyde fixed cells are valid models for studying the light reactions of photosynthesis.Photosynthetic action spectra were determined for brown, green, and red algae by Haxo and Blinks (6), using polaragraphic oxygen determinations. They found that the action spectra for photosynthesis in brown and green algae agreed with the absorption spectra for these algae, but that in red algae the action spectrum for photosynthesis followed primarily the absorption of light by the accessory pigment, phycoerythrin, with chlorophyll appearing largely inactive. Their work, with that of Emerson on the red drop, posed the problem of inactive chlorophyll in plants; a problem finally resolved by the recognition of 2 photochemical systems in photosynthetic electron transport. Kok and Hoch (10) reported the photosynthetic action spectrum of the blue-green alga Anacystis nidulans which showed that light absorbed by chlorophyll a alone was much less efficiently used than light absorbed by both phycocyanin and chlorophyll. The oxidation of P-700 in Anacystis nidulans was driven primarily by chlorophyll a whereas its reduction was ldriven primarily 'by the accessory pigment, an observation which could be most easily explained by the existence of 2 light reactions. Duvsens et al. (4) from action spectra for cytochrome oxidation and reduction in the red alga Porphyridiuin crucntum proposed the existence of 2 photosystems, 1 peaking at 560 nm and the other at 680 nm. These data also suggested that the 2 photochemical systems were related in a sequential manner. Though the 2 light reactions of photosyn-

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