Observe the dilemma of the fungus; it is a plant, but it possesses no chlorophyll. While all other plants put the sun’s energy to work for them combining the nutrients of ground and air into body structure of ground and air into body plane put the sun's energy to work for them combining the nutrients of ground and air into body structure, the chlorophyll-less fungus must look elsewhere for an energy supply. It finds it in those other plants which, having received their energy free from the sun, relinquish it at some point in their cycle either to other animals (like us humans)or to fungi.
In this search for energy, the fungus has become the earth's major source of rot and decay. Wherever you see mold forming on a piece of bread, or a pile of leaves turning to compost, or a blown-down tree becoming pulp on the ground, you are watching a fungus eating. Without fungus action, the earth would be piled high with dead plant life of past centuries. In fact, certain plants which contain resins that are toxic to fungi will last indefinitely; specimens of the redwood, for instance, can still be found resting of the forest floor centuries after having been blown down.