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development and structure i99 



Development and Structure 



247. Vegetation an organism. The plant formation is an organic unit. 

 It exhibits activities or changes which result in development, structure, and 

 reproduction. These changes are progressive, or periodic, and, in some 

 degree, rhythmic, and there can be no objection to regarding them as 

 functions of vegetation. According to this point of view, the formation is 

 a complex organism, which possesses functions and structure, and passes 

 through a cycle of development similar to that of the plant. This concept 

 may seem strange at first, owing to the fact that the common understanding 

 of function and structure is based upon the individual plant alone. Since 

 the formation, like the plant, is subject to changes caused by the habitat, 

 and since these changes are recorded in its structure, it is evident that 

 the terms, function and structure, are as applicable to the one as to the 

 other. It is merely necessary to bear in mind that the functions of plants 

 and of formations are absolutely dififerent activities, which have no more 



-in common than do the two structures, leaf and zone. 



248. Vegetation essentially dynamic. As an organism, the formation 

 is undergoing constant change. Constructive or destructive forces are 

 necessarily at work; the former, as in the plant, predominate until maturity, 

 when the latter prevail. Consequently, it no longer seems fruitful to classify 

 the phenomena of vegetation as dynamic or static. The emphasis which 

 has been placed upon dynamic aspects of vegetation has served a useful 

 purpose by calling attention to the development of the latter. Although it 

 is a quarter of a century since Hult, and more than a half century since 

 Steenstrup, by far the greater number of ecological studies still ignore the 

 problem of development. This condition, however, can be remedied more 

 easily by insisting upon an exact understanding of the nature of the forma- 

 tion than in any other way. It is entirely superfluous to speak of dynamic 

 and static effects in the plant, and the use of these terms with reference 

 to the formation becomes equally unnecessary as soon as the latter is 

 looked upon as an organism. The proper investigation of a formation can 

 no more overlook development than structure, so closely are the two inter- 

 woven. Future research must rest squarely upon this fact. 



249. Functions and structures. The functions of a formation are as- 

 sociation, invasion, and succession : the second may be resolved into migra- 

 tion and ecesis, and the third, perhaps, into reaction and competition. 

 Formational structures comprise zones, layers, consocies, societies, etc., all 

 of which may be referred to zonation, or to alternation. The term associa- 



