The idea of discrete plant communities that can be described, and even named and classified, is very attractive to the inherent neat ness of the human mind and is certainly valuable in the process of mapping areas and assessing their value for conservation and in determining plans for man agement. Whether plant communities have an objective reality as dis-crete entities was energetically debated throughout the 20th century, often turning upon the views of the two American ecologists, Frederic Clements and Henry Gleason, who began the discussion in the 1910s and 1920s. Essentially, Clements regarded the plant community as an organic entity in which the positive interactions and interdependencies between plant species led to their being found in distinct associations that were frequently repeated in nature. He felt that the community assembled itself in a manner comparable to the embryology of an organism and could thus be conceived as an integrated entity. The view proved both attractive and pragmatically useful, forming the basis for early attempts at describing and classifying vegetation by such ecologists as Braun Blanquet in France and Arthur Tansley in Britain