312 GEOGRAPHICAL DISTRIBUTION OF PLANTS. 



Sitka and Norfolk Sound, and extends southwards to Oregon. 

 It seems to be the western representative of the A. serrulata of 

 the southern parts of New England. 



Salicace^e. — Willows are numerous on the east side of the 

 Rocky Mountains, and seem to attain the maximum develope- 

 ment of species in the southern parts of Rupert's Land, but to 

 be less abundant on the Pacific coast, except to the north of the 

 peninsula of Alaska. From Lake Superior to the Arctic Sea 

 they form dense thickets on the shores of every river and lake. 

 It is scarcely possible to note the range of willows, or to collect 

 satisfactory specimens of the species on a rapid journey, as 

 many of them which perfect their catkins before the evo- 

 lution of their leaves, remain undetermined in the herbarium. 

 Of twenty-two species described by Dr. Asa Gray as inhabitants 

 of the Northern States, only S. tristis, Aiton ; S. humilis, 

 Marshall ; & sericea, Marshall ; S. alba, L. ; and S. angustata, 

 Pursh, were not collected by us on our northern voyages. S. 

 uva arsi, S. repens xelfusca, and S. herbacea, which grow on 

 the alps of New Hampshire, extend beyond the arctic circle on 

 both sides of the continent, the latter being one of the most 

 northern plants, as it grows on the north end of Spitzbergen. 

 The other fourteen named by Dr. Gray reach one or more of 

 the northern basins. 



The following were traced from Lake Superior to the arctic 

 circle, or beyond it : S. villosa, S. rostrata, S. discolor, S. 

 viminalis, S. lucida, S. longifolia, S. cordata, S. rigida, S. 

 planifolia, and S. pedicellaris. Some others were not gathered 

 higher than the valley of the Saskatchewan, but their south- 

 ward range included the St. Lawrence basin : as S. Candida ; 

 S. petiolaris, S. rosmarinifolia, S. purpurea, and S.fragilis. 



S. drummondii, S. barattiana, and S. cordifolia were gathered 

 near the elevated sources of the Saskatchewan only, though the 

 last named has been detected by other collectors on the Labrador 

 coast. Salix" sitchensis -is known only as an inhabitant of the 

 island from whence it derives its name. Salix richardsonii 

 and S. acutifolia are common to the Saskatchewan and Mac- 

 kenzie River basins, the former being also an inhabitant of the 

 coast between York Factory and Churchill. 



