Action spectra of the Emerson effect in Chlorella and Navicula reveal peaks at 670 mut, in addition to those at 650 mu (Chlorella) and 630 mmicro (Navicula) attributable to chlorophylls b and c. Thus, excitation of chlorophyll a form "chlorophyll a 670" can supplement, in these algae, the excitation of the form "chlorophyll a 680-700." The effect of the auxiliary pigments in these algae may be mediated by energy transfer to "chlorophyll a 670."