photoperiodism

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photoperiodism The response of an organism to changes in day length (photoperiod). Many plant responses are controlled by day length, the most notable being flowering in many species (see florigen; day-neutral plant; long-day plant; short-day plant). In plants the internal biological clock and the pigment phytochrome are both thought to be involved in the regulation of photoperiodic responses (see also dark period). Activities in animals that are determined by photoperiod include breeding, migration, and other seasonal events. See also melatonin.

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