SUCCESSION 267 



(6) A secondary succession does not begin with the initial stage of 



the primary one which it replaces, but usually at a much later 

 stage. 



(7) At present, successions are generally mesotropic, grassland and 



forest being the ultimate stages, though many are xerostatic 

 or hydrostatic. If erosion continue until the sea level is 

 reached, the ultimate vegetation of the globe will be hydro- 

 phytic. Should the heat of the sun decrease greatly before 

 this time, the last vegetation will be xerophytic, i. e., 

 crymophytic. 



(8) The operation of succession was essentially the same during the 



geological past as it is to-day. From the nature of their 

 vegetation forms, the record deals largely with the ultimate 

 stages of such successions. 



CLASSIFICATION AND NOMENCLATURE 



325. Basis. New or denuded habitats arise the world over by the opera- 

 tion of the same or similar causes, and they are revcgetated in consequence 

 of the same reactions. Similar habitats produce similar successions. The 

 vegetation forms and their sequence are usually identical, and the genera 

 are frequently the same, or corresponding in regions not entirely unrelated. 

 The species are derived from the adjacent vegetation, and, except in alpine 

 and coast regions, are normally different. The primary groups of succes- 

 sions are determined by essential identity of habitat or cause, e. g., aeolian 

 successions, erosion successions, burn successions, etc. When they have 

 been more generally investigated, it will be possible to distinguish subordi- 

 nate groups of successions, in which the degree of relationship is mdicated 

 by the similarity of vegetation forms, the number of common genera, etc. 

 For example, burn successions in the Ural and in the Rocky mountains 

 show almost complete similarity in the matter of vegetation forms and their 

 sequence, and have the majority of their genera in common. A natural 

 classification of successions will divide them first of all into normal and 

 anomalous. The former fall into two classes, primary and secondary, and 

 these are subdivided into a number of groups, based upon the cause which 

 initiates the succession. 



326. Nomenclature. The need of short distinctive names of interna- 

 tional value for plant formations is obvious; it has become imperative that 

 successions also should be distinguished critically and designated clearly. 

 From the very nature of the case, it is impossible to designate each forma- 

 tion or succession by a single Greek or Latin term, as habitats of the same 



