The kinetics of the effects of inductive photomorphogenically active light on etiolated peas have been studied by means of time‐lapse photography. The effects noted include: (1) A light‐induced decrease in the rate of stem elongation, beginning about 6 hr after the light treatment, and ending about 18 hr later. (2) A light‐induced opening of the apical hook, beginning ca. 2–5 hr after light treatment, and reaching its peak rate ca. 6 hr later. (3) A light‐stimulated circumnutation, starting usually about 15–22 hr after the light, and resulting in a decreased period of oscillation (from ca. 86 to ca. 76 min) and an increased amplitude (from 15° total angular displacement to about 40°). (4) A promotion of terminal bud growth, known from previous work to start at about 4 hr after irradiation and to reach a peak about 12 hr later. (5) A “bobbing” movement of the apex, apparently involving reversible hook and stem oscillations, which appears to be of endogenous origin and insensitive to light. These data furnish a kinetic background against which proposed biochemical mechanisms of de‐etiolation can be assessed.

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