294 George E. Nichols, 



larities, but while such subdivisions may be of floristic impor- 

 tance, their significance from the standpoint of ecological plant 

 geography is at least open to question. Thus, it is doubtful 

 whether the "Northern Mesophytic Evergreen Forest" region 

 (characterized in the east by the presence, as the most common 

 species, of white pine, hemlock, jack pine {Pinus Banksiana] 

 and balsam fir), which Shreve ('17) maps as distinct from the 

 "Northeastern Evergreen-Deciduous Transition Forest" region, 

 should be so separated, since throughout this area, as elsewhere 

 in the transition region, climax forests of the deciduous type are 

 commonly encountered in situations which are edaphically suited 

 to their development. Similarly, the "White Pine Region" of 

 New England, as mapped by Hawley and Hawes ('12), while 

 distinct from the standpoint of the forester, does not seem to 

 be so from the standpoint of ecological plant geography. White 

 pine is a frequent constituent of the climatic climax forest 

 throughout the transition region ; but, when growing in pure 

 stands, it probably represents either a temporary association or 

 else an edaphic climax. Not only does it appear unwarranted, 

 from the standpoint of ecological plant geography, to recognize 

 such subdivisions as distinct, but, as elsewhere suggested 

 (p. 261), from this point of view the vegetation of the transi- 

 tion region itself is best regarded merely as a part of the great 

 deciduous forest climatic formation of eastern North America. 



II. THE EDAPHIC FORMATION-COMPLEX OF THE REGION 



A. Primary Formations of the Xerarch Series 



I. The Formation-types of Ordinary Uplands 



a. introductory 



In attempting to formulate the successful series which lead 

 toward and, under favorable circumstances, culminate in the 

 climax association-type of the region, there are three possible 

 sources of evidence: (/) areas in which succession is actually 

 taking place at the present time (or has taken place within com- 

 paratively recent times), as indicated more particularly by the 

 presence of (a) relicts of more primitive associations, or (b) 

 pioneers of more advanced associations than the present ones ; 



