Short-Day Plants (SDP) - Plant Responses to Light-Dark Cycles

These plants only flower or flower more profusely and rapidly when given less than a certain (critical) number of hours of light in a day (24 hours cycle). The critical period, let it be clear, is not 12 hours. It can be for example 10 hours. In that case a plant given less than 10 hours of light (say 8 hours light + 16 hours darkness) will flower. And this critical period is determined experimentally and varies from plant to plant. Short-day plants are found in tropical regions where day length varies comparatively little during the year.