Phytochrome
A phytochrome is a type photoreceptor, or a pigment used by the plant to absorb light, that is found in most plants. This particular pigment absorbs red light and plays a vital role in regulating flowering patterns according to circadian rhythms. It's also crucial to the germination of seeds and the formation of leaves.
The visible light spectrum includes violet, blue, green, yellow, orange, and red. Red is split up into two parts: Red and Far Red. Phytochrome come in two different forms: Pr and Pfr. The protein is synthesized as Pr , which absorbs red light. When the plant is exposed to light it converts into Pfr, which absorbs infa-red light. Once in the dark again, Pfr is reverted back to Pr Presence of Pfr triggers germination, so the plant grows when it has access to the light.
Gaging the amount of constant light the plant receives is how the plant knows what season it is. The photoperiod is the relative lengths of day and night. Plants respond to the photoperiod physiologically (by flowering for example), a process called photoperiodism. Some plants only flower if the photoperiod is more than a certain length. These are called long-day plants. There are also short day plants and day neutral plants (these will flower regardless of the length of day).
Gaging the amount of constant light the plant receives is how the plant knows what season it is. The photoperiod is the relative lengths of day and night. Plants respond to the photoperiod physiologically (by flowering for example), a process called photoperiodism. Some plants only flower if the photoperiod is more than a certain length. These are called long-day plants. There are also short day plants and day neutral plants (these will flower regardless of the length of day).
Black-eyed susans are an example of long day plants
Ponsettia are short day plants
Sunflowers are neutral plants