Forests of Canada. 69 



The peculiarities in the outline of the northward limit of 

 the white cedar and other species of trees, may throw some 

 light on questions as to the direction from which they have 

 migrated or been dispersed. In some cases which the author 

 has studied, the trees appear to have reached the most north- 

 ern limit possible. For example, in its most northern range, 

 the first tender leaves and shoots of the black ash are 

 blighted almost every year by the spring frosts ; the trees 

 are of small size or stunted in height, and only occasionally 

 bear seed. Sir John Bichardson mentions that, on the barren 

 grounds, outlying patches of dying spruces were sometimes 

 met with far out from the verge of the main forest, and that 

 he saw no evidence of young trees springing up beyond the 

 general line of trees; from which he infers that the latter 

 is retreating southward. A similar condition is said to 

 exist in Siberia. 



In tracing the northern limits of several of the trees as 

 laid down on the author's map, it would be observed that 

 the northward variations from the general direction usually 

 corresponded with depressions in the country, while the 

 southward curves occurred where the elevations were 

 greatest. The heigh t-of-land dividing the waters of the St. 

 Lawrence from those of Hudson Bay has a general paral- 

 lelism with the northern limits of many of the species ; but 

 as the watershed is not marked by any great elevation or 

 by a ridge, the circumstance referred to may be owing 

 simply to the accident of its trend coinciding with the aver- 

 age course of the isothermal lines. 



The author divides the trees of the Dominion east of the 

 Eocky Mountains into four groups in regard to geographi- 

 cal distribution, namely: (1) A northern group, including 

 the white and black spruces, larch, Banksian pine, balsam- 

 fir, aspen, balsam-poplar, canoe birch, willows and alder, — 

 these cover the vast territory from the northern edge of the 

 forests down to about the line at which the white pine 

 begins ; (2) a central group of about forty species, occupy- 

 ing the belt of country from the white-pine line to that of 

 the button-wood; (3) a southern group, embracing the 

 button-wood, black walnut, the hickories, chestnut, tulip 



