Leaves can move in response to light
Leaves of many plants move in response to light. This is particularly noticeable in the "sleep movements" that can be observed between day and night in many plants. Sleep movements include closing and/or bending of flowers, and folding of leaves. This short movie shows the light-dependent movement of leaves of an Oxalis plant (often sold in markets as a lucky shamrock plant). The plant in this movie shows the plant over a few days as it is growing under a 12 hr photoperiod. Each frame was captured at 20 min intervals and is played back at 6 frames/sec, which corresponds to 2 hours/sec. In this plant, the transition between the sleeping and waking positions are quite fast, occurring in less than an hour. A biological clock is also involved since, if one looks very closely, the leaf movements can be seen to begin slightly before the lights go on or off. However, unlike the bean and velvet leaf plants shown in other movies, the clock is not very robust in Oxalis and the light response dominates. This can be seen in Oxalis plants in your house. For example, if you turn a bright light on over them in the night when their leaves are closed, the leaves will lift in a short time. Also, if it is a very cloudy day, the leaves may remain in the closed position until the sky becomes brighter.
Note that this movie will keep replaying until you click the pause button on the movie control or hit the spacebar on your keyboard.