Evidence of remembering in plants is most evident in their movements. For example, the familiar ability of sunflower flowers to move in a manner that follows the sun is an obvious response to a diurnal light signal.
Their flowers are directed to the easterly direction in the morning and they follow the sun to the west in the evening. During the subsequent night period, the flowers return to face the east.
These return movements in the dark indicate that the flowers not only track the sun, but they anticipate the return of light, even when the light signal has not yet been restored.
The plants remember the coming of morning.
Kalanchoe flowers also show diurnal cycling – being oriented upward during the day and downward during the night. If the plants are transferred to continuous darkness, the flowers continue the diurnal movements for several cycles.
That plants continue cycling without a light signal indicates that the plants remember the daily light signal even after the signal has been discontinued. They remember the cycling of sunlight.
A similar situation is seen in the diurnal movements of leaves in many plants. For example, the leaves of Albizzia show diurnal changes in leaf position during the day and night.
Again, the positional cycling repeats itself, and if one transfers the plant into darkness the cycling of leaf position continues for several day intervals.
The cycling continues without the light signal, again indicating that the plants remember the cycling of light.
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