Growing on the surface of the forest floor is vegetation of up to about 0.15 metres in height in what is variously described as a moss, soil or cryptogam layer. The ground itself is covered by a layer of dead plant and animal material. In this layer and the underlying few centimetres of the topsoil live innumerable small soil organisms such as bacteria, fungi, algae and microorganisms, which break down the dead organic substances and work them into the soil.