Choosing which models best explain photoperiodic time measurement mechanisms in plants.

Seasonal responses can be triggered by photoperiod changes. To explain photoperiodic time measurement, three main models (hourglass, external coincidence, and internal coincidence) have been proposed based on physiological observations in plants and animals. It has been discussed which model fits best to explain each response. Studies in model plants like Arabidopsis and rice suggest their photoperiodic mechanisms incorporate features that fit more than one of these models.