Word of the day-thermotropism. Thermotropism is a temperature driven movement in plants. In winter, broadleaf evergreens like rhododendron, mountain laurel, and pieris (andromeda) curl or droop their leaves downward to reduce exposure to wind and sun. This limits water loss when the soil is frozen and roots cannot replace moisture. Winter damage is usually dehydration before it is cold. As temperatures rise, cells rehydrate, pressure returns, and leaves lift back into position. This is a normal,