Which of the following may be the substitute of photoperiodism?

Photoperiodism was first investigated and recorded by W. W. Garner and H.A. Allard, plant physiologists in Tobacco plant in 1906. according to their response to day light, plants were grouped as long day plants, short day plants, and day neutral plants. A plant can be made to flower throughout the year by providing favourable photo period but besides these, lowering of temperature can also induce flowering in plants. This is known as vernalization and is done by exposure to prolonged cold  weather is known as vernalization.