temperatures at night, then thaw again in the early morning. Because a curled leaf has less of its surface area exposed to the sunlight, the leaf will thaw more slowly than it would if it were unfurled. Slower thawing minimizes damage caused to leaf cell membranes by ice crystal formation. Although there is little known about the molecular mechanisms of this rolling behavior, turgor pressure is responsible for the leaf movement. The exact stimulus for this output is not understood, but it is known that freezing cold temperatures causes an influx of water to the leaf petiole. As the turgor pressure increases, the leaves roll up, making it tighter to the stem. The leaf also droops perpendicular to the ground. There are predictions on the mechanism of this behavior. Regional changes of cell hydration can cause the inward curling. Another prediction is a change in cell wall physiology. These predictions are very broad, indicating the need for further research. There are currently two hypotheses to why Rhododendrons do this. The first is that the shape is more effective for snow shedding and better protects the more sensitive areas. Another hypothesis for leaf rolling called the desiccation theory, circulating in recent years, is to prevent membrane and light damage. In a 2017 study about cold stressed Rhododendron leaves showed that photosynthetic proteins decreased, while proteins for cell permeability increased. The same study showed the highest increase in proteins were responsible for transcription and translation regulation. Thermotropic response in rhododendron leaves protects cells by changing leaf shape and protein levels. Thermotropism in roots The roots of some plants, including Zea mays, have been shown to bend differently when exposed to different temperature conditions. In general, growing roots tend to bend away from warmer temperatures, and towards cooler temperatures, within a normal range. It has been suggested that this growth behavior is beneficial because in most natural environments, soil closer to the ground's surface is warmer in temperature, while deeper soil is cooler. Experimentation with maize has demonstrated the existence of thermotropic responses in roots, with stronger responses seen when the thermal gradient increases. Positive thermotropism, or growth towards higher temperatures, was shown to occur at lower temperatures, with the strongest response observed at a temperature of 15 C. As the temperature increases, the strength of the response decreases. With continually temperature increases, a lack of thermotropic response is observed and occurs once