However, some the genera open their stomata only during the evening or night. These genera can undertake what is called the `CAM-photosynthetic pathway' and characteristically have very thick leaves. Hence, the humidity must be high during the evening and at night for genera such as Cattleya, Vanda, Dendrobium, and certain species of the Cymbidium genus. Because these genera do not open their stomata during the day, it really does not matter to them what the daytime humidity is like.