Biology / Unit 11 Bio 2553 short lesson, about 20 seconds
Photoperiodism
Captions available
The idea
Photoperiodism is a plant's use of the phytochrome system to track night length, timing flowering and dormancy to season rather than temperature alone.
In practice
A short-day plant flowers once nights exceed a critical length in late summer, using the ratio of active to inactive phytochrome sensed at dawn.
Where people slip
Day-neutral plants exist too — not every species regulates flowering by photoperiod at all.
Your place on the trail
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