1910] Heller—Mammals: Alaska Expedition, 1908. 359 
The evident floral areas of the region are four: the forest, 
tundra, littoral, and alpine. These divisions, with the exception 
of the alpine, are based chiefly on soil conditions. The tundra 
occupies wet swampy ground that the forest cannot invade, the 
complete saturation beine fatal to tree growth. This is well 
shown by the stunted hemlocks and spruces growing on the edges 
of these tundras, where they have been dwarfed by the unfa- 
vorable conditions. The forest occupies the drier ground ex- 
cepting a narrow littoral strip subject to periodical submergence 
and areas of very reeent formation. These littoral formations 
are of a gravelly construction and are, except for short periods, 
the driest areas to be found in the region. The Alpine Zone 
includes the area above timber-line which, owing to its low tem- 
perature, cannot support conifers. The tundra, forest, and 
littoral associations are all parts of the Hudsonian. The forest 
and the alpine associations have already been characterized 
sufficiently. 
The tundra oceurs as islands in the forest area and consists 
chiefly of a heavy covering of mosses and shrubs which hold 
much moisture. The characteristic shrubs of this area are Vac- 
ciniwm uliginosum and Myrica gale. A dwarf Salix is also quite 
characteristic. The heathers, Phyllodoce and Harrimanella, are 
usually an important part of the tundra association. About 
the edges of these bogs a scattering border of such shrubs as 
Cladothamnus, Viburnum, Pyrus sitchensis, Vaccinium ovalifo- 
lium, and Menziesia are usually to be found; but they are not 
invaders, not even to the extent of Tsuga or Picea. 
The littoral zone is characterized by species which are partial 
to salt-water influences, namely: Elymus mollis, Senecio pseudo- 
arnica, Lathyrus maritimus, and Arenaria peploides. Associated 
with these, but of less maritime habits, are two large umbellifers, 
Heracleum and Coelopleurum, and the shrubs Sambucus race- 
mosa, Ribes triste, Rubus spectabilis, a shrubby Salix, and Alnus 
sitchensis. With these species are usually associated a host of 
herbaceous plants characteristic of these gravelly areas. In a 
region so mountainous and aretie as Prince William Sound, land 
slips oceur frequently. These produce many changes in the 
definition of plant associations. The littoral changes due to the 
