I know plants have a cycle not only in a host of macroscopic and microscopic
behaviors, but in their ability to respond to light.
The sequence of day and night length changes across the year mandate that identical day and night lengths occur at two times of year. In North Carolina, for example, there are only 11 hours of daylight in mid-February and again in mid-November. If 13 hours of continuous darkness was a simple cue to me to change my seasonal pattern of behavior, I would be receiving confusing signals as this event occurs twice each year. However, the overall pattern of change is quite different: in mid-February, each successive day length is slightly longer, whereas in mid-November, each successive day length is successively shorter in duration. So, how plant organisms use the pattern of changes in day/night length to solve the paradox that daylength is equal twice a year.