SUMMARYThe structurally-organized association ofChlorella xanthellaand a species ofStreptomycesinto an actinolichen is independent of temperature over at least a range from 18 to 26 C and can occur in constant as well as variable temperatures. Actinolichen formation is light-dependent, requiring a minimum of 275 ft-c and light is optimal at about 900 ft-c. The active wave lengths of light are probably at or below the blue end of the spectrum. Actinolichens can be formed on nutrient solid surfaces or in liquid medium under shake conditions.