346 PAST succession: the ceneosere. 



consisted of but three stages, but was perhaps abeady differentiated into 

 hydrarch and xerarch areas. It had taken on its typical character, in as much 

 as earlier climax forms became subordinate and assumed the r61e of develop- 

 mental stages. The sere already represented a succession of higher life-forms 

 as well as of higher taxonomic forms, a character which it still retains, though 

 the great differentiation of life-forms in the Angiosperms overshadows the 

 earlier stages in which life-form and taxonomic form are more nearly corre- 

 lated. The interrelations of life-form and reaction must have been decisive 

 then as now. The tendency of the later great floras of the Paleophytic and 

 Mesophytic to become subordinate is less obvious, but it is still clearly shown 

 by the behavior of relict communities of Equisetum, Selaginella, ferns, and 

 cycads in existing seres. 



Geosere and eosere. — The development of the vegetation of the earth from 

 the first appearance of commimities of marine algse in the Eophj^ic down to 

 the present is comprised in the geosere. As a matter of fact, however, it is 

 simpler and more convenient to regard the geosere as limited to the develop- 

 ment of land vegetation. Thus conceived, the geosere is marked by four 

 great stages corresponding to the four great floras and their respective eras. 

 Each of these stages has its own peculiar climax and its ontogenetic or serai 

 development. Since each climax marks an era or eon, the major course of its 

 development during the era is termed an eosere. As already noted, the Ceno- 

 phytic era with its climax of Angiosperms is marked developmentally by a 

 Ceneosere or Angeosere. The Mesophytic era, characterized by Gymno- 

 sperms, comprises the Meseosere or Gymneosere, and the Paleophytic with its 

 Pteridophytes, a Paleosere or Ptereosere. The development of vegetation 

 in the Eophytic era might perhaps be termed the proteosere or thalleosere, but 

 it is at present too hypothetical to warrant a special term. 



While each eosere comprises all the ontogenetic processes of its climax, it 

 also bears a phylogenetic relation to the eosere which precedes and the one 

 that follows it. In their phylogenetic relation, the four eoseres constitute 

 the geosere. The species and genera of one eosere give rise to those of the 

 next, and the flora of the latter produces in its turn that of the next eosere. 

 The geosere in consequence possesses two kinds of organic continuity, the one 

 marked by the evolution of new floras, the other by the succession of climax 

 vegetations. In short, the geosere comprises the whole evolution of plant 

 forms and the complete succession of plant communities. 



To avoid the undue multipUcation of terms, it seems necessary at present to 

 use the terms geosere and eosere in a concrete as well as an abstract sense. The 

 terms have been used above to refer to the successional phenomena of the whole 

 world. In this sense there is but one geosere for the world and a single eosere 

 for each era. Concretely, however, the differentiation of climate and hence 

 of vegetation must have led to the production of climaxes different for various 

 regions. Clearly, the course of the geosere, and of each of its eoseres, must 

 have differed in tropical and polar regions, or at least in glaciated and non- 

 glaciated regions, even before the Permian period. In later periods this 

 differentiation must have become more marked, resulting in a relatively large 

 nimiber of regional eoseres in the Cenophytic era. The geosere in general 

 is considered only under its divisions, as marked by the vegetative eras, 

 namely, Ceneosere, Meseosere, and Paleosere. The course of the geosere in 



