Epiphytic Orchids are grown perched high in the trees clinging to branches or in the trunk apex of the tree. They derive their nutrients from the air, rain, and any decaying vegetation, which the roots can contact. Epiphytic Orchids have specialised aerial roots, which have a white spongy layer of cells called velamen. This protects the inner root tissues and absorbs water. These roots will also often dangle free in the atmosphere. �Lithophytic Orchids are seen covering the bases and forks of trees or filling crevices in rocks, and absorb a maximum supply of nutrients from decaying mosses. �Terrestrial Orchids are seen under the ground, having a symbiotic relation with a special fungus, which in turn supports the orchid with the essential nutrients.