320 GEOGRAPHICAL DISTRIBUTION OF PLANTS. 



of plants gathered by Mr. Campbell at Pelly Banks, and 

 Dr. Asa Gray's important Botany of the Northern States, 

 have contributed to our knowledge of the distribution of 

 species, and have been severally had recourse to. 



The first zone extends on the eastern side of the conti- 

 nent from latitude 45° to 55°, or it comprehends the St. 

 Lawrence and Saskatchewan basins : it rises obliquely, 

 in accordance with the course of the isothermal lines, in 

 going westward, and on the Pacific coast it includes the 49th 

 and 58th parallels, or Vancouver's and Sitka Islands. It 

 is subdivided into three districts ; viz., the eastern forest 

 country, the eastern prairies, and the country west of the 

 crest of the Rocky Mountains. 



The second zone comprehends all the country lying 

 between the arctic circle and the extremities of the conti- 

 nent in latitude 72°. It was not found practicable, owing 

 to the way in which the herbaria were formed, to separate 

 the barren ground species from those growing in the woody 

 country, and the zone has been made to include three dis- 

 tricts, one of which is Kotzebue Sound, where 273 species 

 have been collected by Chamisso and others.* 



The Rocky Mountain ridge, between the 52nd and 57th 

 pai'allels, has been made a second district of this zone, as 

 many arctic species go southwards along the elevated crest 

 of the ridge. I have not been able, however, to separate 

 the species collected by Drummond in the lower valleys of 

 the ridge from those gathered high up on the peaks. From 

 the untiring diligence and unrivalled quickness of eye of 

 this celebrated collector, we may consider the district as 

 well explored ; and had the vertical ranges of the species 



* Mr. Seeman, who was employed as botanist in the Herald's late 

 voyages to that quarter, has made a much more ample herbarium of 

 the north-west coast; but as he has just arrived in England as these 

 pages are passing through the press, I can avail myself only partially 

 of his researches for the improvement of the table. 



