1910] Heller —Mammals: Alaska Expedition, 1908. 357 
The only characteristically Hudsonian tree of general distri- 
bution is Tsuga mertensiana. Chamaecyparis nootkatensis, which 
is also a Hudsonian tree, is of sporadic occurrence in the region 
and on that account of little zonal significance. No typically 
Hudsonian shrubs, with the exception of Vaccinium uliginosum, 
were observed in the region, those occurring being widespread 
Boreal forms, together with a few stragglers from the Arctic- 
Alpine Zone. 
The proportion of shrubs and perennial plants which oecur 
from this region south through the Canadian Zone to the coast 
of Washington is large, nearly 90 per cent. One conifer, Picea 
sitchensis, accompanies these wide-spread species. This large 
proportion of boreal forest species occurring at the limit of tree 
erowth makes the definition of a Hudsonian Zone very difficult. 
Sinee so many trees and shrubs extend through the whole Boreal 
region below the Arctie-Alpine Zone, the combination of the 
Canadian and Hudsonian zones into a Boreal forest gives us a 
term of more distributional significance and allows us to ignore 
the Hudsonian in districts where it is ill-defined. 
The following species of trees and shrubs occur along the 
coast from Prince William Sound south at least to the coast of 
Washington : 
Tsuga heterophylla Pyrus diversifolia 
Picea sitchensis , Pyrus sitchensis 
Myrica gale Echinopanax horridum 
Alnus sitchensis Cornus canadensis 
Ribes bracteosum Menziesia ferruginea 
Aruncus sylvester Vaccinium ovalifolium 
Rubus spectabilis Sambucus racemosa 
The occurrence of this association of plants along this im- 
mense length of coast is in my opinion due rather to humidity 
than to temperature conditions. The rainfall in this coast strip, 
which is the heaviest in extra-tropical America, averages nearly 
the same throughout its whole length. On the coast of Wash- 
ington it ranges from 80 to 130 inches. This is about the range 
of the rainfall at the few stations in Prince William Sound where 
records have been kept, and it is also close to that of the rainfall 
of the intermediate stations on the coast. The differences in 
temperature existing between the southern and the northern 
