Presidential Address: Some aspects of soil ecology

[First paragraph...]
It is well known that in most soils vast numbers and great variety of living organisms may be found. They range in complexity from the simplest of single-celled animals plants and bacteria, through to burrowing mammals and higher plants, and include representatives of almost every major group of organisms. Photosynthesis by the green plants that grow on the soil surface is the source of energy upon which the whole population ultimately depends, and most of the organisms are decomposers of plant tissue.