Researchers obtained the phase-shifting response of the petal movement rhythm in the succulent plant Kalanchoe blossfeldiana (darker curve) by giving a 2-hour light treatment at various times after transferring plants from cycles of 12 hours light and 12 hours dark to continuous darkness (Web Figure 20.5.A).

Web Figure 20.5.A   Characteristics of the phase-shifting response in circadian rhythms. Researchers obtained the phase-shifting response of the petal movement rhythm in the succulent plant Kalanchoe blossfeldiana (darker curve) by giving a 2-hour light treatment at various times after transferring plants from cycles of 12 hours light and 12 hours dark to continuous darkness. The curve shows the delay or advance of petal movement rhythm compared with that of plants receiving no exposure to light. The response of photoperiodic timing in the short-day plant Chenopodium rubrum (red goosefoot) (lighter curve) was obtained by a 6-hour light treatment at different times after transfer to darkness. The curve shows the delay or advance of the rhythm of flowering response to a night break. (Data for Kalanchoe from Zimmer 1962. Data for Chenopodium from King and Cumming 1972.)

The darker curve shows the delay or advance of petal movement rhythm compared with that of plants receiving no exposure to light.

The response of photoperiodic timing in the short-day plant Chenopodium rubrum (red goosefoot) (lighter curve) was obtained by a 6-hour light treatment at different times after transfer to darkness.

The lighter curve shows the delay or advance of the rhythm of flowering response to a night break. (Data for Kalanchoe from Zimmer 1962. Data for Chenopodium from King and Cumming 1972.)