266 THE FORMATION 



(6) Each pioneer produces about itself a tiny area of ecesis and 



stabilization for its own offspring, for the disseminules of its 

 fellows, or of invaders. 



(7) Species propagating by offshoots, or producing relatively im- 



mobile disseminules in small number, usually show effective 

 ecesis, as the offspring appear within the area of the reaction 

 of the parent forms. 

 V. Stabilization. 



(i) Stabilization is the universal tendency of vegetation. 



(2) The ultimate stage of a succession is determined by the domi- 



nant vegetation of the region. Lichen formations are often 

 ultimate in polar and niveal zones ; grassland is the final vege- 

 tation for plains and alpine stretches, and for much prairie, 

 while forest is the last stage for mesophytic midlands and 

 lowlands, as well as for subalpine regions. 



(3) Grassland or forest is the usual terminus of a Succession ; they 



predominate in lands physiographically mature. 



(4) The limit of a succession is determined in large part by the pro- 



gressive increase in occupation, which makes the entrance of 

 invaders more and more difficult. 



(5) Stabilization proceeds radiately from the pioneer plants or 



masses. The movement of offshoots is away from the parent 

 mass, and the chances of ecesis are greatest near its edges, in 

 a narrow area in which the reaction is still felt, and the 

 occupation is not exclusive. 

 VI. General laws. 



(i) The stages, or formations, of a succession are distinguished as 

 initial (prodophytia) , .intermediate (ptenophytia), and ulti- 

 mate (aiphytia). 



(2) Initial formations are open, ultimate formations are closed. 



(3) The number of species is small in the initial stages; it attains a 



maximum in intermediate stages ; and again decreases in the 

 ultimate formation, on account of the dominance of a few 

 species. 



(4) The normal sequence of vegetation forms in succession is: (l) 



algae, fungi, mosses; (2) annuals and biennials; (3) peren- 

 nial herbs; (4) bushes and shrubs; (5) trees. 



(5) The number of species and of individuals in each stage increases 



constantly up to a maximum, after which it gradually de- 

 creases before the forms of the next stage. The interval 

 between two maxima is occupied by a mixed formation. 



