The long wavelength forms of chlorophyll a.

When Euglena gracilis is cultured with light of low intensity (ca. 250 ft-c), an absorption band at 695 mmu is formed in an amount equal to about 20 per cent of the total chlorophyll absorption in this red region. An equally large proportion of C(a)695 is observed in Ochromonas danica, irrespective of light intensity. Other algae tested appear to contain approximately 3 to 5 per cent of their chlorophyll as C(a)695; this proportion does not increase as strikingly with lowering of the light intensity as it does in Euglena. C(a)695 bleaches more readily than the other chlorophyll forms both reversibly, in whole cells, and irreversibly, in homogenates. Cells containing a large proportion of C(a)695 have a fluorescence maximum at 708 mmu, as contrasted to the 687 mmu maximum in other algae. Occasionally, old cultures of Euglena contain cells with an absorption band at approximately 710 mmu. This absorption band is quite stable in aqueous extracts; when the pigment is transferred to ether an equivalent amount of pheophytin a is found to be present. Conditions leading to the formation of the 710 mmu absorption band are not yet known.