2 MUSEUM BULLETIN NO. 26. 



period, the different species establishing themselves in regions where the 

 climatic conditions met their specific requirements. 



The glacial period, furthermore, explains readily a few striking 

 features in the present distribution of Canadian plants, viz., the occur- 

 rence of identical species in localities separated by hundreds or even 

 thousands of miles of land, across which, under present conditions, 

 migration is impossible. Thus, a number of species occur in the Rocky 

 Mountains which are identical with species living in Arctic Canada or 

 in Labrador and Eastern Quebec, but occurring nowhere else in the 

 Dominion. These facts may be explained in the words of Darwin, as 

 follows : 



As the warmth returned (after the glaciation had reached its height) the 

 arctic forms would retreat northward, closely followed up in their retreat by the 

 productions of the more temperate regions. And as the snow melted from the 

 bases of mountains, the arctic forms would seize on the cleared and thawed ground, 

 always ascending higher and higher, as the warmth increased, whilst their brethren 

 were pursuing their northern journey. Hence, when the warmth had fully returned, 

 the same arctic species, which had lately lived in a body together in the lowlands 

 . . ., would be left isolated on distant mountain summits (having been exter- 

 minated on all lesser heights) and in the arctic regions. . . . 



With regard to British Columbia, a few words may be said in explana- 

 tion of the diversity of the flora. Although glaciation may not, at any 

 time, have been general, it is nevertheless highly probable that its flora, 

 at the time of the glacial period, was subjected to the necessity of migra- 

 tion in a north and south direction. At any rate, the British Columbia 

 flora is most closely related to the flora south of the province, genera 

 and species occurring which extend as far south as to New Mexico 

 and California. 



The most characteristic feature of the flora of British Columbia is, 

 however, not so much its general relationship to the flora to the south 

 as the existence of different floristic provinces more or less sharply 

 defined. The existence of different "floras" is due not only to the 

 highly diversified climatic conditions, but perhaps still more to the 

 presence of mountain chains and desert-like areas which act as barriers 

 checking the free migration of the plants. 



Arctic Zone. Botannically, the Arctic Zone is the region lying 

 north of the tree line. In Canada it extends far to the south of the 

 Arctic circle, especially in the eastern parts of the Dominion. Its 

 southern limit is, roughly, a line running from the estuary of the Macken- 

 zie river to the mouth of the Churchill river, on the west coast of Hudson 

 bay. East of Hudson bay, the tree line runs from about lat. &Z on 

 Richmond gulf to the mouth of George river on the eastern shore of 

 Ungava bay, and from there in a southeasterly direction along the coast 

 of Labrador to Hamilton inlet. 



The arctic flora of Canada is very closely related to that of Europe, 

 especially the Scandinavian, a very great proportion of the arctic 



