It was recently suggested (Boney & Corner, i960,1962a) that, contrary to the theory of complementary chromatic adaptation, the accessory pigment phycoerythrin might not be involved in photosynthesis by sporelings of the intertidal red alga Plumaria elegans (Bonnem) Schm. but is used primarily as a means of protecting the plant from excess green light in the wave-band 500–540 mμ. This work, however, was done with one species only, and concerning the wider question of marine red algae in general, it seemed possible that the role of phycoerythrin might vary with ecological distribution. Thus, plants completely submerged and thereby excluded from most red light would use their accessory pigments for photosynthesis (energizing chlorophyll a indirectly); but plants adapted to long periods of normal daylight would be similar to Plumaria in relying to a much greater extent on chlorophyll a alone for photosynthesis, and use their accessory pigments as protection against inhibitory green light.