60 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
THE HUDSONIAN ZONE. 
This is the highest of the timbered plant zones, its average altitude 
in Washington being from 1,500 to 2,800 meters (5,000 to 7.500 feet). 
The most widespread and characteristic tree in all the northwestern 
mountains is the subalpine fir (dies lasiocarpa) (Pl. XVIT). In 
the Olympic and Cascade mountains this is always accompanied by 
the black hemlock (7suga mertensiana), a tree which recurs locally 
in the Bitterroots of Idaho, but which is unknown in the Blue Moun- 
tains save on a single peak. It is not known whether this tree occurs 
in the Okanogan Highlands. In the Olympic and Cascade moun- 
tains the Alaska cedar (Chamaecyparis noothatensis) is likewise a 
characteristic tree, but it does not occur eastward from the latter 
range. The white-bark pine (Pinus albicaulis) also belongs to this 
zone, and reaches a higher altitude than any other Washington tree. 
It is absent from the Olympics, but occurs nearly throughout the 
Cascade Mountains, and appears again on the higher peaks of the 
Blues and Bitterroots. 
Comparatively few shrubs and herbs are definitely limited to this 
zone. Among the more conspicuous are an azalea (Rhododendron 
albiforum), a currant (Ribes howellii), and the western mountain 
ash (Pyrus occidentalis). In places the bear grass (Yerophyllum 
tenax) occupies acres of ground, but this plant occasionally occurs as 
low as the Transition zone. 
In the following table is given a list of the characteristic Hud- 
sonian species, showing their known appearance on the principal 
peaks of the Cascade Mountains, namely, Mounts Stuart, Rainier, 
Adams, St. Helens, Hood,t Mazama,” and Shasta.©§ Only small col- 
lections have been made on Mount Baker, and for this reason the 
species known to occur in the Cascade Mountains between the 48th 
and 49th parallels are lumped for comparison. The table also shows 
which species occur in the Arctic regions, in the Olympic Mountains, 
in the Blue Mountains, in the Rocky Mountains as a whole, and in 
the Sierra Nevada. 
@ Howell, Thomas. The Flora of Mount Hood, Mazama, vol. 1, pp. 28-48, 1896. 
6 Coville, Frederick V. The August Vegetation of Mount Mazama, Mazama, 
vol. 1, pp. 170-208, 1897. 
¢ Merriam, C. Hart. Results of a Biological Survey of Mount Shasta, North 
American Fauna, no. 16, 1899. 
