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 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 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 éssential identity of habitat or cause, e. g., aeolian 
successions, erosion successions, burn successions, etc. When they have 
been more gencrally investigated, it will be possible to distinguish subordi- 
nate groups of successions, 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 
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 cattse 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 
