58 ■ CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



These instances are not to be confused with those illustrated b}' 

 plants of wide altitudinal range, like Castilleja ininiafa, which occurs 

 in all the zones from Upper Sonoran to Arctic, as do also Castilleja 

 angusti folia, Aquilegia formosa, Heracleum lanatum, Hypericum 

 ir:ouleri, Achillea millefolium, and others. 



The condition that has determined this strange nonconformity in 

 the altitudinal or zonal relations of the species al)ove mentioned is 

 perhaj^s to be sought in the lower winter temperatures of the interior. 

 This factor alone ma}^ tend to confine a species to the lowest zonal 

 l^osition in which it can maintain its existence. 



THE CANADIAN ZONE. 



This is the most illy defined of all the life zones in AVashington, 

 merging into the Transition below and the Hudsonian above. Its 

 most characteristic tree is perhaps the western white pine (Pinus 

 ruonticola), but in 'Washington this tree is not abundant. In the 

 Olympic and Cascade mountains the amabilis fir (Abies amahilis) is 

 also a characteristic tree, as is its near relative, the noble fir [A. nohi- 

 7is), found in the Cascades from Mount Stuart southward. Apart 

 from these trulv characteristic trees, the white fir (Ahies f/7'andis) 

 and the western hemlock {Tsvga heterophylla) (PI. XYI) both find 

 their best development in the Canadian zone, but both also are not 

 rare at sea level. The dominant tree of the Humid Transition zone, 

 the red fir, also thrives in the companv of its Canadian relatives. 



On the eastern slopes of the Cascades, and more especially in the 

 mountains of eastern Washington, two other trees appear in the Cana- 

 dian zone, the Engelmann spruce {Picea engelmanni) and the western 

 larch {Larix occidentalis) , while the amabilis and noble firs disappear. 



A characteristic plant association of this zone is that of the lodge- 

 pole pine, a form of Pinus contorta, ^\\\\c\\ often forms dense forests. 

 The trees are remarkably uniform in size, seldom exceeding 1 foot in 

 diameter and GO feet in height. Such forests are often very exten- 

 sive, the one species making up 90 per cent of the timber. AMiile 

 most al)undant in the Canadian zone, groups of the lodgepole pine 

 occasionally occur isolated in yellow jnne forests. 



There are but few plants in Washington confined to the Canadian 

 zone. The somber depths of these moist forests, however, induces a 

 luxurious carpet of mosses and a vegetation which is largely erica- 

 ceous. Among the more plentiful shrubs are the blue huckleberry 

 {Vaccininin ocali folium), Menziesia ferruginea. Pachystima myrsi- 

 nites, the trailing Ruhus nivalis, and the dwarf cornel {Cornus 

 canadensis) . 



