It was cold and windy today. I found myself walking quickly down the street, with my head down and hands tucked deep into the pockets of my coat trying to keep as little of my skin exposed as possible. It made me think of the Rhododendron. In the winter, it's large leaves droop down and curl backward so the soft permeable underside is protected, while the outer, waxy side is exposed to the elements.
What they are doing is called thermotropism. Thermotropic movement is the movement of a plant or plant part in response to changes in temperature. The dry winter air and winds can cause moisture loss from the stomata on the underside of the leaf, so the leaf curls to protect itself. Once you see the Rhododendrons looking like this, you know it's cold!
I look forward to the day when these leaves uncurl because it means warmer weather is here to stay!