24 BULLETIN 1423, U. S. DEPARTMENT OF AGRICULTURE 
Some species of lichens form leaf-like expansions (foliaceous), 
some are cup shaped, some closely encrust the surface on which they 
grow (crustaceous), and others are shrublike (fruticose), the 
branches in this case being either cylindrical or flattened. Their 
colors vary from almost white to greenish gray, yellow, orange, 
brown, or a purplish black. Changes in color are greatly influenced 
by degrees of light and moisture or the nature of the habitat. In 
Alaska the fruticose lichens form the bulk of the winter forage. 
(Pis. 14-17.) 
For their growth lichens require moisture, light, and heat, and 
probably derive some inorganic substances from the base upon 
which they grow, but most lichens probably take a smaller propor- 
tion of their food from the substratum and a larger proportion 
from the air than do the higher vascular plants. They take carbon 
dioxide from the air in the processes of nutrition, build up lichenin, 
a substance similar to starch, and return free oxygen to the atmos- 
phere. When wet and in a partially decomposed condition, some 
lichens are often of a gelatinous consistency. The thallus of some 
species contains a bitter principle, which in a few instances may 
make the plant unpalatable to stock. 
LICHEN OCCURRENCE AND DISTRIBUTION 
On Alaskan coast ranges the best lichen growth is often found on 
west and north exposures. In thick stands of forest or brush very 
little of it occurs, but at the edges or in openings in the forest, or in 
scattering tree growth, a luxuriant lichen cover may usually be 
found (pi. 12, fig. 1). On moist tundra flats of favorable soil and 
atmospheric conditions, as on Nunivak Island, lichen growth may be 
abundant, both in volume and density (pi. 12, fig. 2). On the 
average summer tundra range of the coast, however, the herbaceous 
and shrub vegetation competes predominantly with the lichens. On 
the more rugged inland country the competition is reduced and the 
lichens often become the predominant vegetation. Here the best 
lichen cover of value for grazing is on the lower slopes, in coves, and 
hollows, and at the heads of creeks. The best individual growth 
occurs particularly in depressions on slopes and in swales and is 
most luxuriant in hollows between and at the bases and sides of 
hummocks. Certain valuable species, however, of comparatively 
short height often occur abundantly on the tops of hummocks in 
favorable situations and under minimum competition. On rocky 
upper slopes and tops of ridges the lichen cover becomes scattering 
and is usually small or dwarfed. 
Even among the best of lichen types a pure stand does not occur, 
either with reference to class of vegetation or to individual species. 
Generally an admixture of lichens with other vegetation is found, 
as species of browse, mosses, and sedge. Often in the lichen stand 
there may occur a considerable portion of such mosses as Sphagnum 
and Polytmchum. On most of the winter ranges the lichens aver- 
age 50 per cent of the cover, although some forage types occur that 
may contain as much as 90 per cent lichen vegetation. 
Within the stand the lichens grow more or less intermingled in 
a solid mat, with species intermixed generally, but often by indi- 
