= 348 Part IV. Chapter ı. 
species peculiar to this territory are Braya pilosa, Boykinia (Therafon) Richard- = 
sonii, Artemisia androsacea (= A. senjavinensis), Saussurea alpina (= 5. sub- Be 
sinuata), Salix glacialis, while many north temperate plants reach here’ the 
arctic region which are excluded from eastern arctic America by the rigors of 
the climate. 
a) Tundra Formation. 
The tundra region of Alaska is low and gently undulating (see plate VII, 
Its flora is quite varied. Besides the numerous mosses and heathers and many 
small berry-bearing plants are dwarf willows, birches and alders. The alders 
attain the greatest size but grow in isolated clumps, often 6 to 8 feet high. 
The ground is frozen a few inches below the surface and the heavy, sponge- 
like covering of vegetation is constantly saturated. Upon such soil grow 
Cassiope tetragona, Andromeda polifolia, Vaccinium vitis-idaca, Arctous (Ma 
rania) alpina, Ledum palustre, Artemisia arctica, Rubus chamaemorus, Rubus 
arcticus, Betula nana, Alnus sinuata, Loiseleuria (Chamaecistus) procumbens 
and Nardosmia (Petasites) frigida‘): Eastward in the Barren Grounds ol 
the Mackenzie basin occur Cassiope tetragona, Ledum palustre, Rhododendron 
lapponicum,. Arctostaphylos uva-ursi, Dryas integrifolia and several dwarf wil- 
lows. The crowberry Empetrum nigrum, occurs in the greatest abundance 
along the northern border of the more or less stunted timber at tree limit. 
Occasional high bluffs on the coast in exposed situations are bleak and 
bare, but besides these there is scarcely an area not covered by low, matted 
vegetation. Numerous small ponds are irregularly distributed over the Alaskan 
tundra and around them the vegetation is ranker than elsewhere. It appears 
that a favorable combination of soil, shelter from winds, and full exposure t0 
the sun have more to do with the development of flowering plants in polar 
regions than parallel of latitude. For in polar regions the sunlight is less in- 
tense, as well as more constant, lasting as it does for half of the year, but 
is also more diffuse, the solar rays being forced to pierce a much thicker 
atmospheric stratum. The stems of such plants as grow under these con- 
ditions are more highly developed than in alpine regions, floral colors are paler, 
the foliage is less rigid and thick, and the blossoms are smaller. These points 
are of physiognomic importance in recording the ecologic character of t 
vegetation of the American north polar region. Dwarf growth, general xeroph- 
ily and the predominance of mosses and lichens are noteworthy features 0! 
the tundra. The type of vegetation determines the peculiarity of the tundra. 
Thus we have, as characteristie plant associations, a moss a Polytrichum 
tundra, a Lichen tundra, and the facies is conditioned by the climatic € 
ditions which control, whether we have a Cladonia tundra (C/adonia rangt 
Jerina, Sphaerophoron coralloides), a Platysma tundra (Platysma cucullatun, 
Cetraria islandica etc.) or an Alectoria heathery. Where the climatie 
ı) OsGoop, WILFRED H.: Results of a biological Reeonnaissance of the Yukon River Region. 
North American Fauna No. 19. U.S. Division Biological Survey 1900 Se 
