Abstract
Studies were made on the developmental responses of flue-cured tobacco, Bright Yellow and Hicks, to the various warm photoperiod of 18°C with cool dark period of 13°C or 8°C. Results obtained were as follows; 1. The developmental responses of tobacco plant is not influenced by the cool temperature during the long dark period corresponding to the short period, but is accelerated to a marked degree by that corresponding to the long photoperiod. So the cool dark period in long day seemed to have retardative effects on the photoperiodic response. 2. According to the results that the number of leaves of the plant exposed the light interruption during the cool dark periods was almost equal to that of the 12hr day-length, it may be unable to expect the long-day effect equal to the effect of illumination during all night.
