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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. 52° 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 
