THE TRANSITION FROM FILAMENTOUS TO TWO-DIMENSIONAL GROWTH IN FERN GAMETOPHYTES. III. INTERACTION OF CELL ELONGATION AND CELL DIVISION

Periodic cell divisions were induced in gametophytes of Pteridium aquilinum by daily irradiation with white light. In white-dark cycles, the rate of cell division was promoted by increased time in white light; cell elongation was not affected. The time of transition to two-dimensional growth (days to 5% 2-D) was closely associated with the mitotic rate. For white-red cycles, the rate of elongation was controlled by the intensity of red light (wavelengths over 550 nm). This increased elongation delayed the initiation of 2-D development. In both cases the rate of transition to 2-D growth was correlated with the amount of elongation per division.