An Age-Dependent Change in the Response of Fern Gametophytes to Red Light.

When gametophytes of Onoclea sensibilis are grown in darkness a filament of a few cells develops which elongates at a constant rate. Low dosages of red light given at the beginning of growth increase the rate of elongation. After about 12 days in darkness, however, gametophytes show a decreased growth rate when given red light.