258 



George E. Nichols, 



Midway between these two regions (see map, Fig. i), is 

 situated the Transition Forest Region, a broad zone in which, due 

 to the overlap in the ranges of the southern and northern cHmax 



Figure i. — Alap of eastern North America, to show position of Cape 

 Breton Island with reference to the Transition Forest Region. 



extremes. Moreover, especially in these intermediate forms, the struc- 

 tural dissimilarities upon which the manuals lay stress in attempting to 

 differentiate two distinct species, are far from satisfactory in their applica- 

 tion. In the present paper no attempt is made to distinguish P. rubra 

 from P. mariana, although it is appreciated that much of the upland 

 spruce may perhaps well be referred to the former "species." 



