(8,12). During continued culture over many generations in FR light, we observed increases in growth rate and in the Chl/PC ratio, usually occurring in a concomitant and stepwise fashion. From such cultures, we were able to establish clones which differed from the parent in pigment composition. We have described six clones, which are presumed to be spontaneous mutants selected under the photosynthetically restrictive condition of FR illumination (13). As compared to the parent, all mutants showed better performance (growth) under FR light for which Chl is the principal absorber but poorer perform-

ABSTRACT

Emerson and coworkers (4,5,8) discovered that low quantum yields of photosynthesis observed at long wavelength (near 700 mr) could be increased by supplemental or background light of shorter wavelength. The Emerson enhancement effect has been studied further in the belief that it should provide a key to the role of the various pigments. Considerable attention has been devoted to the reality and generality of the effect and to spectra of the shortwave component of enhancement. All such spectra support the view that the short-wave component includes one or more of the accessory pigments characteristic of the plant used: chlorophyll b, chlorophyll c, phycocyanin, phycoerythrin, fucoxanthol, and the chlorophyll a-673 (2,8,9,14).

Growth of Anacystis nidulans (Richt.) Drouet & Daily in wavelengths of light predominantly absorbed by chlorophyll a causes a dramatic lowering in chlorophyll content and in the chlorophylllphycocyanin ratio. A limit to the effect is reached in far red (680 nm) light where the ratio chlorophylllphycobilinogen falls to <0.3. A special water bath for culture tubes was illuminated by tungsten‐halogen lamps through far red (>650 nm)filters; it gave the same extreme pigment ratio together with a high specific growth rate of 2.5 day‐1. Compared with normally pigmented cells there are three features which accompany the low‐chlorophyll condition of far red light. At 677 nm relative quantum efficiency increases but action decreases. Synthesis of total pigment and total cell material in far red light also decreases. These observations suggest that the low chlorophyll response to far red light reflects an incompetence rather than an adaptation.

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