244 PLANT LIFE. 



These wood-lichens, Ever^nia and Ramalina, as well 

 as Usnea, Alecioria, and Parmelia physodes^ are by no 

 means without real importance to the forest (see p. 308). 



The Old Man's Beard Lichens belong to the genera 

 Usnea and Alectoria. They are generally confined to 

 old long-established woods. The Usneas are short, 

 upright, grey-green tufts. Their stems and branches 

 are round and not flattened or irregular, as in the 

 Evernia group. The Alectorias are drooping or hanging 

 and much longer (6 inches to i foot), of a darker brown- 

 green, and thinner and more slender. They are thus 

 able to yield to the wind and their smooth, almost 

 shining surface will prevent any friction with the air. 

 The cups are very seldom formed in Usnea and 

 Alectoria but the soredia are easily carried off by the 

 wind. Both of them seem to prefer unhealthy trees, 

 probably because the cork is not being properly thrown 

 off by a vigorous increase in thickness. 



The cup and trumpet lichens or Cladonias are exceed- 

 ingly pretty little plants generally under two inches in 

 height. They vary in colour between pure white and grey 

 green, but a few of them are almost brown. They consist 

 of two distinct parts. The cup, trumpet, or small, erect, 

 simple or branched stalks (podetid)^ upon which are the 

 head of spores or masses of grey soredia, and the flat, 

 grey-green lobes, which grow over the soil and carry on 

 the work of carbon assimilation and of absorption. 

 Their classification depends upon the colours of the 

 cups and upon the character of the little lobes or scales 

 of the ground portion. In the Reindeer-moss lichen 

 (^Cladonia rangiferind) there is no ground part, the 

 stalks having developed into erect branching tufts like 

 small shrubs generally 3 or 4 inches high. All these 

 branches are slightly bent over at the tip and occasion- 



