248 INTRODUCTION TO BOTANY 
Although usually grayish green in color, some of the lichens are 
yellow, red, brown, or even black. Lichens can endure severe 
drought, cold, and prolonged exposure to intense light and to 
strong winds; hence it is evident that they can live under con- 
ditions which would be destructive to most kinds of plants. 
On account of this 
ability to undergo 
severe conditions, 
lichens are found 
atas great altitudes 
and throughout 
as great a range 
north and south 
as are any plants. 
They may remain 
dormant through 
long periods of un- 
favorable weather 
and, when favora- 
ble moisture and 
BR temperature return, 
Fic. 193. A common lichen (Parmelia) upon the almost immedi- 
bark of the shagbark hickory ately assume the 
Note the expanded and flat part of the lichen, also the greenish appear- 
cups in which spores of the fungus part of the lichen F a 
are formed ance which indi- 
cates their renewed 
activity. The lichen known as reindeer moss is brittle and 
pallid when dry, but when moist, it is green and soft. 
Those lichens which adhere very closely to their support 
and are scale-like are called crustaceous; those that adhere less 
closely and are leaf-like are foliose; and those that branch and 
are partially free from their sub-stratum are friticose. Foliose 
forms are common upon rougher-barked trees and upon old 
fences, crustaceous forms grow upon smooth-barked trees and 
upon stones, while fruticose forms grow upon the ground or 
hang from branches of trees. 
