650 JOURNAL OF FORESTRY 



of species characteristic of the various biological zones into which the 

 Dominion can be divided, and in this way aiding the botanist to orient 

 himself. 



There are ten such zones recognized, and under each the principal 

 and characteristic tree, shrub, and herbaceous flora is enumerated. It 

 should, perhaps, be noted that the differentiation into zones, which 

 the authors adopt, is open to criticism, lacking in uniform biological 

 basis, and in some cases calling for further subdivision. 



Generally speaking, the Canadian plants may all be considered 

 immigrants after the ice age subsided, with a small exception of 

 endemic plants on the Coast Range. One striking feature in the dis- 

 tribution, explainable by the manner of the migration after the glacial 

 period, is the occurrence of identical species in localities separated by 

 hundreds and even thousands of miles of land, across which, under 

 present conditions, migration is impossible. This distribution has espe- 

 cially reference to arctic and alpine species. 



The arctic, treeless zone, the southern boundary of which towards 

 the east dips very considerably, contains very few species of American 

 origin, they are mostly closely related to European in the East and 

 Asiatic in the West; in other words, the flora is circumpolar, com- 

 posed almost exclusively of perennial plants, largely occurring in 

 bunches or dense mats. A distinction is made between the tundra, as 

 the more southern and physiologically wetter part, and the more 

 northern, rocky, more or less dry part. 



While the whole zone has characteristic woody plants of prostrate 

 willows or shrubby birches {nana and glandulosa), on the tundra 

 ericaceous species of Ledun, Rhododendron, Vaccinium, Arctosta- 

 phylos and Empetrum are most prominent. 



The sub-arctic forest zone, a rolling country, as yet mainly un- 

 settled, with numerous bogs and lakes, which in the East is bounded 

 by the white and red pine northern limit, or roughly by a line from 

 Anticosti to the south end of Lake Winnipeg, is a coniferous forest 

 of mainly white and black spruce and banksian pine with aspen, balsam 

 poplar, paper birch and larch and balsam fir. The prevalence of berry 

 shrubs are its most striking characteristic. The bog flora, as well as 

 the whole sub-arctic flora, is remarkably uniform, combining species 

 of arctic and more southern distribution. Only a small water lily, 

 Castalia tetragonal, is found in the sub-arctic zone only. 



The hardzvood forest zone to the south of the sub-arctic comprises 

 the more or less settled country and the commercial timber area in the 



