Studies on the Nature of the Endogenous Rhythm Affecting Photoperiodic Response of Biloxi Soybean

Abstract

1. Biloxi soybean (Glycine max [L.] Merr.) plants were subjected to seven photoinductive cycles which varied in length from 24 to 96 hours. In experiment 1 the length of both the photoperiod and the dark period were varied. Plants were exposed to photoperiods of 8, 16, or 32 hours' duration. While the 8-hour photoperiod was given at both 27⚬ and 12⚬C., the latter two were supplied at the lower temperature only. In experiment 2 the plants received a photoperiod of constant duration (8 hours at 27⚬ C.), but the dark periods varied in length from 8 to 64 hours. In additional groups each dark period was interrupted by 30 minutes of high-intensity light, either at its mid-point or 16 hours after its beginning. 2. Flower-bud initiation showed a rhythmical pattern in the photoperiodic reaction. With an 8-hour photoperiod at high temperature (27⚬ C.) the maxima were shown with cycle lengths 24, 48, and 72 hours long, and the minima with cycle lengths of 36 and 60 hours. 3. Low temperature during the 8-hour photop...