The light requirement for germination in spores of the fernThelypteriskunthii (Desv.) Morton was fully satisfied by a long period of continuous red light or partially by intermittent, short periods of red light. Red light‐potentiated spore germination was inhibited by brief far‐red light irradiation, indicating phytochrome involvement. Repeated exposure of spores to prolonged red and short far‐red irradiations, or exposure of red‐potentiated spores to far‐red light after an extended period in darkness, led to their escape from inhibition of germination by far‐red light. Prolonged irradiation of spores with blue light before or after red light treatment partially antagonized the effect o