Peat moss (genus Sphagnum) grows mostly in bogs. Peat mosses are favored by gardeners for their ability to increase the water-holding capacity of soils. Due to large, dead cells in their leaf-like parts, they are able to absorb five times as much water as cotton plants. Peat mosses are also used as damp cushions by florists to keep other plants and flowers damp. Species of Sphagnum also have medicinal purposes. Certain aboriginal people use peat mosses as disinfectants and, due to their absorbency, as diapers. Peat moss is acidic and is an ideal dressing for wounds. During World War I, the British used more than one million wound dressings made of peat moss. Native North Americans used species of the genera Mnium and Bryum to treat burns. In Europe species of the genus Dicranoweisia have been used to waterproof roofs.