Photoperiodic control depends on which environmental factor?

• A. Day length
• B. Night length
• C. Temperature
• D. Humidity

Answer: (B)

Photoperiodic responses are governed by how long the night lasts. The plant uses the duration of uninterrupted darkness as the cue that triggers seasonal changes like flowering or dormancy. During daylight, light exposure shifts photoreceptors into a form that resets the clock, and the length of the subsequent dark period determines the signaling state the plant uses to decide its response. Temperature and humidity can influence growth, but they are not the primary signal for photoperiodism.