CLASSIFICATION OP SERES. 173 



succession is a series of biotic successions, i. e., a cosere; and the climatic cycle 

 or succession is a series of coseres, i. e., a clisere or an eosere. This reveals 

 the basic objection to a classification grounded upon causes. As is obvious, 

 it not only obscures the developmental subordination of the three kinds of 

 succession, but it also ignores the fact that so-called biotic successions may 

 be caused by topography, climate, or artificial agents, man, and animals. 

 These may also be agents in topographic succession as well, though less fre- 

 quently. As has been often pointed out in the discussion of initial causes, 

 the same sere or cosere may result from a number of different causes. More- 

 over, as is shown in detail in Chapter XII, climatic and topographic factors 

 are inextricably mingled in the causation of eosere and clisere. This is inevit- 

 able from the coincidence of deformational, sun-spot and volcanic cycles as 

 shown in figure 26 and plate 57. Furthermore, in all periods with peat or coal 

 seres and coseres, such as the Pleistocene, Cretaceous, Pennsylvanian, etc., 

 the same development may result from flooding due to increased rainfall or to 

 a local sinking of the region. 



Another source of confusion lies in the fact that biotic succession is stated 

 to be due to plants and animals. The r61e of plants is that of reaction upon 

 the habitat, as a consequence of which one stage succeeds another. Such a 

 reaction is tj^jical of all succession, and the latter would be impossible without 

 it. Man and animals, on the contrary, are initial causes, as is topography, 

 and have httle to do with reaction. Hence, as already shown (Chapter III), 

 it is imperative for the understanding of vegetational development to distin- 

 guish initial causes, topographic, climatic, and biotic, from ecesic or continu- 

 ative causes, of which reaction is the most striking. Moreover, a plant may 

 itself be an initial cause, in such instances as the one mentioned, where Cuscata 

 produced bare area again by completely destroying the pioneers of a dune 

 sere. This confusing double use of the term biotic is well illustrated by the 

 statements of Paulsen (1912 : 104) and Matthews (1914: 143). Speaking of 

 the sand desert, Paulsen says that the development from stable to unstable 

 desert through the agency of man must be considered a biotic succession. 

 Matthews, in describing the water sere in Scotland, states that there seems to 

 be suflBcient evidence for regarding the main determining factors as entirely 

 biotic. In the former, the cause of the bare area is biotic, in the latter, topo- 

 graphic; in both the ensuing course of development is due to the reaction of 

 plants, and is necessarily biotic. 



Crampton (1911 : 20; 1912 : 4) has adopted Cowles's classification, as have 

 also Crampton and MacGregor (1913: 180), but his application of the terms 

 appears to be more or less divergent. The regional successions of Crampton 

 seem to include the small and recent swings of climate, such as are found in 

 the coseres of peat-bogs (1911 : 22), rather than the great eoseres of geological 

 history. His topographic successions seem to be the existing ones due to local 

 topographic initial causes (1911 : 29) and not those of Cowles, which are related 

 to the vast regional changes comprised in an erosion cycle. Crampton appears 

 to ignore biotic successions altogether, especially the vast number of secondary 

 successions, regarding the local topographic succession as well-nigh imiversal 

 while Cowles ascribed much the greater importance at present to his biotic 

 successions (1911 : 172). Crampton's treatment is still further complicated 

 by the distinction between stable or paleogeic and migratory or neogeic for- 



