Photoperiodism

From Freepedia

Photoperiodism is the physiological reaction of organisms to the length of day or night. It occurs in animals and plants.

Many flowering plants use the pigment phytochrome to sense seasonal changes in day length, which they take as signals to flower. Broadly, flowering plants can be classified as long day plants, short day plants, or day neutral plants. Long day plants require a certain amount of daylight to initiate flowering, so these plants flower in the spring or summer. Conversely, short day plants will flower when the length of daylight falls below a certain amount. Day neutral plants do not initiate flowering based on photoperiodism; some may use temperature (vernalization) instead.

Other instances of photoperiodism in plants include the growth of stems or roots during certain seasons, or the loss of leaves.

Some birds use photoperiodism to prepare for a migration or for the cold of winter. In some mammals, the time of estrus is regulated by photoperiodism.