Photoperiodism was first characterised in:
The response of plants to changes in relative lengths of day and night
They phenomenon of photoperiodism was first discovered by Garner and Allard (1920, 22) in the tobacco plant. They observed that Maryland Mammoth, the variety of tobacco could be made to flower only by reducing the light hours with artificial darkening. It could be made to remain vegetative in winter by providing extra light.