136 SUCCESSION 



erosion continue until the sea level is reached, the 

 ultimate vegetation of the globe will be hydrophytic. 

 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 today : from the 

 nature of their vegetation forms, the record deals 

 largely with the ultimate stages of such successions. 



CLASSIFICATION AND NOMENCLATURE. 



New or denuded habitats arise the world over by the oper- 

 ation of the same or similar causes, and they are revegetated 

 in consequence of the same reactions. Similar habitats 

 produce similar successions. The vegetation forms and 

 their sequence are usually identical, and the genera are fre- 

 quently the same, or corresponding im 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 successions 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 subordinate groups of suc- 

 cessions, in which the degree of relationship is indicated 

 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 se- 

 quence, 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 in- 

 to a number of groups, based upon the cause which initiates 

 the succession. 



The need of short distinctive names of international 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 



