Compost heap bacteria. Coloured scanning electron micrograph of bacteria covering the surface of a piece of decomposing leaf on a compost heap. Compost is made by allowing a heap of vegetable trimmings, non-seeding weed plants and grass mowings to degrade. The resulting brown, crumbly compost is dug into soil to provide plants with nutrients. Here, only very decomposed leaf material around the dividing walls remains. The surface is covered by various coccal (spherical) and rod-shaped saprophytic bacteria. These bacteria feed on the dead leaf, breaking it down into its constituent elements. Magnification: x1,000 at 6x6cm size.