AMPHI-ATLANTIC ZONATION, NEMORAL TO ARCTIC 123 



was considerably different from modern conditions. Even if some of the 

 species probably are very old, their re-combination into plant communities 

 thus is comparatively recent. The elements of the Boreal or Taiga zone, for 

 instance, must have survived the latest Glacial Epoch in several widely separ- 

 ated refugia where ecological conditions and types of vegetation were 

 necessarily different in various respects from those prevailing in the present 

 Taiga. It is astonishing that the products of the re-combination of these ele- 

 ments is so uniform, and that such a great zonal parallelism exists in areas as 

 much as 8000 miles apart in longitudinal direction. 



The history of the vegetation is the evident starting-point of ecology. On 

 the other hand, the ecological requirements of both single taxa and whole 

 plant communities, as reflected in their present zonal distribution, put down 

 limits which historical deduction should not overstep without very strong 

 reasons. Therefore, this somewhat lengthy exposure of largely well-known 

 facts may be of some value as a background for the historical discussions of 

 these problems. 



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