HORNBEAM, HAZEL, BIRCH AND ALDER 



99 



izes the European white or silver birch^a closely related but dis- 

 tinct species — which is one of the few trees that grows among the 

 heather, in fact an abundance of seeds widely distributed by the 

 wind characterizes most of the birches and is especially noticeable 

 in the changing cycles of vegetation recorded in Pleistocene de- 

 posits which contain the history of bogs and moors changing into 

 forests and back again. 



Fig. 19. Sketch Map Sho\ving Ancient and Modern Distribution 

 or the Birches 



Northern limits of Arctic birches. 



Northern and southern limits of white birches. 



X X X X X X Range of other birches (subsections Costatae and Betulaster). 

 • • # • Fossil occurrences. 



A most thrilling story could be written of the part played by 

 the birch bark canoe in the exploration and development of the 

 northern half of our continent, Parkman gives something of this. 



