ACTION SPECTRUM FOR THE APPEARANCE OF THE 520 MILLIMICRON DIFFERENCE BAND IN ILLUMINATED CHLORELLA CELLS.

An action spectrum of the 520 mmu difference band in Chlorella is determined using dim illumination. Pigment (or pigments) absorbing most strongly at and above 680 mmu, probably the so-called "long-wave forms" of chlorophyll a appear to be the primary sensitizer of the 520 mmu effect.

Fluorescence and Absorption Changes in Chlorella Exposed to Strong Light: The Red Band.

The reversible decrease in the apparent intensity of the main red absorption band of chlorophyll a at 680 mnu upon strong illumination of Chlorella cells, described by Coleman and Rabinowitch in 1957, is shown, by a polarization method, to be due to an increase in the fluorescence yield. True absorption changes are observed at 657 mnu (positive) and 648 mnu (negative).