Stomata make gas exchange possible while helping to control the loss of water. To conserve water during dry times, the stomata remain closed to reduce the loss of water vapour. The number of stomata on the epidermal surface can tell a lot about a plant. Usually, a high concentration of stomata indicates fast growth and a wet climate. Lower concentrations of stomata indicate lower rates of photosynthesis and growth or adaptations for dry weather. Stomata are useful to drought-threatened plants because they can close to prevent dehydration.