A terrarium is a miniature garden in an artificial environment, in which small plants and animals may be kept as ornament or for educational purposes. Fish bowls, small fish tanks, large bottles, and carboys are often employed as containers for terrariums; such vessels permit the necessary entrance of light for photosynthesis by the plants, and are suitable for display. The most important aspect of a terrarium is its relatively high humidity, maintained either by using a container with only a small aperture or by keeping the container covered. The humid atmosphere enables mosses and other sensitive woodland plants to flourish.