Question

If short day plants (e.g., tobacco) are kept under short day conditions during the summer season when day light is far much more than 12 hours, what would be the effect on the flowering of such plants? Give reason for your answer.

Answer 1

A plant that requires a long period of darkness, is termed a "short day" (long night) plant. Short-day plants form flowers only when day length is less than about 12 hours.
Many spring and fall flowering plants are short-day plants, including chrysanthemums, poinsettias, and Christmas cactus. If these are exposed to more than 12 hours of light per day, bloom formation does not occur. For example, a short-day plant that requires >12 hours of uninterrupted darkness to initiate flower production will still produce a flower if it is shielded from light for some time during its 10-12 hours of daylight exposure; it will not, however, produce a flower if it is exposed to light for a period of time during.