Further Aspects of the Photoperiodic Responses of Sequoia gigantea

1. The stimulatory growth effects of long photoperiods and the depressive effects of short photoperiods in Sequoia gigantea are apparently operative through a dark-dependent mechanism. 2. The short-day effects may be largely nullified by daily interruptions of the long dark period with short light breaks. 3. Significant increases in primary-branch growth were attained in plants growing on long photoperiods when the long light period was interrupted with daily 1-hour periods of either darkness or low-intensity light.