Short-day plants flower when the day is shorter than a critical maximum. Long-day plants flower when the day is longer than a critical minimum. Plants actually respond to the length of the dark period, rather than the light. Interruptions of the light period had no effect on flowering, but interruptions of the dark period inhibited the effects of long night treatments. Phytochrome acts as a photoreceptor.
Temperature can modify the amplitude of the fluctuation.
The part that is grafted is called the scion, while the part that receives the graft is called the stock.