64 NORTH AMERICAN FAUNA. (No. 16. 
PLANTS OF CANADIAN ZONE—continued. 
(1) Species known to occur in Cunadian zone on Shasta—Continued. 
Spircea douglasi. Tritelia ixioides. 
Spraguea umbellata. Vaccinium occidentale. 
Stachys ingrata. Vagnera stellata. 
Stellaria crispa. Veratrum californicum. 
Tofieldia occidentalis. Viola blanda. 
(2) Species restricted to Vanadian zone. 
Abies shastensis. Lilium parvum. 
Aconitum columbianum. Madia bolanderi. 
Allium validum. Pentstemon deustus. 
Alnus sinuata. Pentstemon gracilentus. 
Arnica longifolia. Pinus monticola. 
?Corallorhiza bigelovi. Pinus murrayana. 
Delphinium sonnei. Pyrola pallida. 
Drosera rotundifolia. Senecio trigonophyllus. 
Erigeron inornatus. Tofieldia occidentalis. 
Gentiana simplex. Vaccinium occidentale. 
Habenaria leucostachys. Viola blanda. 
Habenaria unalaschensis. 
(3) Species common to Canadian and Transition zones. 
[See p. 61.] 
(4) Specics common to Canadian and Hudsoniun zones. 
Arctostaphylos nevadensis. 
Campanula wilkinsiana. 
Castanopsis sempervirens. 
Castilleja miniata. 
Chrysothamnus bloomeri. 
Holodiscus discolor. 
Hypericum anagalloides. 
Ligusticum grayi. 
Mimulus primuloides. 
Monardella odoratissima. 
Phlox douglasi diffusa. 
Ribes cereum. 
Spraguea umbellata. 
Stellaria crispa. 
HUDSONIAN ZONE. 
The Hudsonian zone is the highest of the timber belts. Its sinuous 
upper border rises on the high ridges to inclose the narrow tongues of 
dwarf prostrate trees that push up on the warmest southwesterly expo- 
sures to an extreme altitude of 9,800 feet, but between the ridges it 
dips down a thousand feet or more, and is difficult to fix with precision. 
The lower border slightly overlaps the upper limit of Shasta firs. Two 
species of trees, and only two, grow in this zone—the black alpine hem- 
lock (Tsuga mertensiana) and the white-bark pine (Pinus albicaulis). 
The hemlock is restricted to local spots, while the white-bark pine forms 
a practically continuous belt, as already explained (see p. 42). On 
warm southwesterly slopes the Hudsonian reaches from 7,500 or 7,800 
up to 9,500, or in extreme cases to 9,800 feet. 
