In the regions where ultra-violet waves go beyond 3022 A., the approximate limit of uv irradiation in nature, were directed on a culture, the green algal cells were killed. These lethal regions appear as decolorized cells in the green algal plate at the wave lengths of 3022, 2967, 2894, 2804, 2753, 2699, 2652, and 2536 A. Wave lengths longer than 3022 A., that is the wave lengths of 3130, 3341, and 3650 A. had no appreciable lethal effect upon the algae. Yet by the thermocouple measurements a greater intensity of light was directed on the cultures at wave lengths 3130 and 3650 A.