Bog-moss (Sphagnum), a large genus of mosses of world-wide distribution, having a structure specially adapted to their aquatic mode of life. They only possess roots when young, the base of the stem decaying into peat while its upward growth is continued by a succession of side shoots or "innovations." The stem has externally several layers of large cells destitute of protoplasm, with large perforations, by which water rapidly rises through the plant. The leaves also, which are only one cell thick, have similar cells surrounded by meshes of smaller ones containing chlorophyll. On removal from the water the whole plant rapidly dries and bleaches. It is extensively employed in packing plants and in cultivating orchids and bog-plants.