<P> Two quotes illustrate the contrasting views of Clements and Gleason . Clements wrote in 1916: </P> <P> The developmental study of vegetation necessarily rests upon the assumption that the unit or climax formation is an organic entity . As an organism the formation arises, grows, matures, and dies . Furthermore, each climax formation is able to reproduce itself, repeating with essential fidelity the stages of its development . </P> <P> while Gleason, in his 1926 paper, said: </P> <P> An association is not an organism, scarcely even a vegetational unit, but merely a coincidence . </P>

Which of the following is an example of an event leading to primary succession