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 

 at as 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 

 temperature return, 



FIG. 193. A common lichen (Parmelia) upon the 

 bark of the shagbark hickory 



Note the expanded and flat part of the lichen, also the 



cups in which spores of the fungus part of the lichen 



are formed 



almost immedi- 

 ately assume the 

 greenish appear- 

 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 fruticose. 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. 



