350 WHITTAKER 



into a meaningful pattern according to his general perspective and chosen 

 ecological concepts. Some conclusions of historians of man are pertinent, al- 

 though the vegetational historian may be spared concern with influences of 

 culture, personality, choice, and volition — except those affecting the historian. 

 History is an imaginative reconstruction of the past which is scientific in its 

 determinations but approaches the artistic in its formulation; and history is 

 more genuinely scientific in spirit as it takes into account the inescapable 

 limitations on its objectivity and rigor (Muller, 1954, p. 35). It is no criticism 

 of Clements', Braun's, and Wang's interpretations of eastern forest history 

 to observe that these are human conceptual reconstructions which cannot be 

 simply inherent in, or uniquely determined by, the information which they 

 bring into a pattern of interpretation. It is relevant to Clements' system, how- 

 ever, that vegetational evolution is not a phylogeny. 



Natural communities are not organisms, except in Whitehead's sense in 

 which "organism" is equivalent to "system." Their manner of function and 

 organization, their interrelation and classification, their development and 

 maturity, and their evolution present problems which are distinct from, and 

 significantly different in character from, those of individual biological or- 

 ganisms. In Clements' system the complex organism became the central unify- 

 ing theme, the background concept from which the meanings of other con- 

 cepts were to be understood. The organismic analogy has been accepted by 

 some authors (Phillips, 1934-1935; Tansley, 1920, 1935; Allee et al., 1949), 

 rejected by many others (Gleason, 1917, 1926; Gams, 1918; Meusel, 1940; 

 Schmid, 1942; Ellenberg, 1950, 1954); but in current writing it is not the 

 central concept of vegetational understanding — it is seldom referred to. The 

 treatment of environment as cause and community as effect has been criticized 

 as a fundamental weakness of Clements' system (Egler, 1951 ) ; probably Clem- 

 ents would not have ventured the parallel statement: environment is the cause, 

 and the plant is the result. The cause-and-effect view seems poorly suited to 

 the manner in which the community and environment are interrelated; a 

 "transactional" approach to the functional system formed by community and 

 environment may be more appropriate (Whittaker, 1954). A central concept 

 different from Clements' complex organism and its cause-and-effect relation 

 to environment, and different from the kind of synthesis of plant-animal 

 ecology attempted by Clements and Shelf ord (1939), appears in contemporary 

 ecology. It is the concept of the functional whole formed by community and 

 environment— the ecosystem. 



Conclusion: a changing outlook. Scarcely a major feature of Clements' 

 system as an intellectual structure remains intact, in this author's view. To 

 observe this alone, however, may be to underestimate both the lasting signifi- 

 cance of Clements' contribution and the real significance of the change that 

 has occurred. Talcen all together, the changes in ecological conceptions dis- 

 cussed amount to a general re-orientation of viewpoint in a field of science. 



