314 Proceedings Portland Society Natural History 



corded them by phytogeographers. In the present paper 

 an attempt will be made to clarify the relations of the vari- 

 ous formations before assigning the Penobscot Bay region 

 to any one of them. 



It is a generally accepted conclusion in current ecologi- 

 cal literature that there exist in eastern North America two 

 great climatic unit areas, each of which is characterized by 

 a particular type of climax forest. These forest areas 

 comprise : 



(1) the Eastern Deciduous Forest which centers and 

 attains its optimum development in the lower Ohio basin and 

 the southern Appalachians, with the beech (Fagus grandi- 

 folia), sugar maple (Acer saccharum), chestnut (Castanea 

 dentata), tulip (Liriodendron Tulipifera), sycamore (Pla- 

 tanus occidentalis), red oak (Quercus rubra), white oak 

 (Quercus alba), white ash (Fraxinus americana), and sev- 

 eral species of Juglans and Carya as the character trees. 

 Of these the beech and maple are often cited as the most 

 prominent. (See Cooper (4) in this connection). 



(2) the Northeastern Evergreen Coniferous Forest, 

 which centers and attains its optimum development in east- 

 ern Canada; with the balsam fir (Abies balsamea), the black 

 spruce (Picea mariana), white spruce (Picea canadensis ), 

 and paper birch (Betula alba var. papyrifera) as the char- 

 acter trees. 



Between these two areas lies a broad zone where the 

 ranges of the southern and northern climax trees overlap, 

 thus creating an intermediate, telescoped type of vegeta- 

 tion — a tension zone in which the various species are in 

 active competition. In general the limits of this Transi- 

 tion Forest Region, as it is called, may be said to lie be- 

 tween the northern limits of the deciduous Acer saccharum 

 and the southern limits of the coniferous Abies balsamea 

 (see map, Figure 2). The Transition region, thus delim- 

 ited, coincides to a remarkable degree with a distinct floris- 

 tic region, the Canadian. However, even though the flora 



