INTRODUCTION 



I. GENERAL PHYTOGEOGRAPHIC RELATIONS OF THE 



REGION 



Viewed from the standpoint of ecological plant geography, the 

 vegetation of the forested portions of eastern North America, 

 north of southern Florida, comprises two great climatic forma- 

 tions : the Deciduous Forest Formation and the Northeastern 

 Evergreen Coniferous Forest Formation. Viewed from the 

 standpoint of floristic plant geography, it is possible to subdivide 

 the vegetation of this area still further (in this connection see 

 especially Transeau '05, Harshberger '11, Shreve '17), but from 

 the ecological point of view, as will be emphasized later, the 

 advisability of such subdivision is at least open to question. 



The deciduous forest formation attains its highest and most 

 typical development in the lower Ohio basin and the southern 

 Appalachians, where the climax forests are made up almost wholly 

 of decidtreus trees. These include a wealth of species, prominent 

 among which are beech (Fogns grandifolia) and sugar maple 

 (Acer saccharnm), chestnut (Castanea dentata) and tulip 

 {Liriodcndron Tiilipifcra), red oak (Qiiercus rubra), white oak 

 (QitercKS alba), hickor>' (especially Carya alba), and white ash 

 (Fraxinus amcricana) . The evergreen coniferous forest forma- 

 tion attains its optimum development in middle-eastern Canada. 

 Here the climax forests are relatively poor in species, consisting 

 mainly of balsam fir (Abies balsamea), white spruce (Picea cana- 

 densis) and black spruce^ (Picea mariana), with which is asso- 

 ciated the paper birch (Behda alba papyrifera). 



^ In all the current manuals a distinction is made between the black 

 spruce and the red spruce (Picea rubra). After several years of experi- 

 ence in the north-woods, the writer is obliged to confess his inability to 

 differentiate with certainty between the two, an inability which he finds 

 to be shared by many other botanists. It is his opinion that the red spruce 

 at best should be regarded merely as a variety of the black spruce, the 

 status which it formerly held. To be sure, the small, impoverished bog 

 form of this tree (the typical P. mariana of the manuals) does appear very 

 distinct when compared with the large, thrifty upland form (which typi- 

 fies P. rubra) ; but there are all sorts of intergradations between these two 



