REINDEER GRAZING INVESTIGATIONS IN ALASKA 23 
The species of Cetraria and Stereo caul on are also important but 
less abundant. Browse and dried herbaceous vegetation are taken 
to some extent and occasionally some of the mosses. 
THE LICHEN PLANT 
The plants that furnish the bulk of the forage on winter range 
are lichens. They are entirely different from herbaceous and shrub 
vegetation in character and in reaction to grazing use. They do 
not, like the herbaceous vegetation, furnish a renewed forage crop 
from year to year, but require a long period of years to recover 
from one season's cropping. Lichens grow very slowly and are of 
limited height, but attain a very great age. They are of com- 
paratively delicate structure, infirmly anchored to the soil, and are 
readily removed either by trampling or picking by hand. Under 
summer conditions they often become dry and brittle and are then 
easily destroyed. When moist or wet they are of almost spongy 
texture and then less easily injured. 
The lichen plant is a composite organism — an alga and a fungus 
living together. The relationship has become so intimate that 
lichens are often regarded as autonomies or morphological units 
rather than symbiotic colonies of algae and and fungi. The frutiti- 
cation of the lichen is that of the fungus, and reproduction takes 
place by means of the spore. Many lichens also multiply asexually 
by means of soredia, produced by the chlorophyll-bearing cells, go- 
nidia, which belong to the algae, the soredia escaping from the 
lichen thallus usually in the form of a fine powder, and germinating 
immediately to form new plants. A third mode of reproduction is 
by the distribution of fragments of the plants by action of wind or 
animals. 
GROWTH HABITS OF LICHEXS 
Lichens grow under a great variety of conditions of climate and 
habitat. (Pis. 12 and 13.) Their general distribution both verti- 
cally and horizontally is extensive. All are capable of enduring 
desiccation for long periods without losing their vitality. Their 
height is limited, but the size to which they may attain varies with 
individual species and habitat. Along the Alaskan coast, the aver- 
age growth of the mixed stand is 4 or 5 inches, although in places a 
10-inch height has been found (pi. 13, fig. 2). Some species are of 
diminutive size and consequently of little or no use for grazing; 
others are of luxuriant growth and highly valuable. 
Lichens grow chiefly on soil, on rocks or stones, and on the 
bark of trees; but they also grow frequently on decayed logs and 
on mosses, and sometimes on the thalli of other species. According 
to the base upon which they grow they are classified as terricoline 
(on soil), corticoline (on bark), saxicoline (on rocks), and musci- 
coline (on mosses). Those most important for forage in Alaska are 
largely of terricoline habit. The essentially saxicoline, muscicoline, 
and corticoline species, with a few exceptions, are mostly of diminu- 
tive size or of low form adhering closely to the substratum, and 
therefore of low grazing value. 
