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Cetraria Oakesiana. Tuckm. (Plate V, 3.)— Thallus foliaceous and 

 compact; it adheres more closely to the substratum than C. ciliaris and C. 

 lacunosa. It is a light straw color, beneath it is brown. The lobes are finely 

 cut and lie quite fiat, except at the margins, where they are curled and are 

 covered with white soredia. 



Cetraria Islandica (L.) Ach. (Fig. 2.) Unlike 

 C. ciliaris and C. lacunosa this species has a fruti- 

 cose thallus; it is the familiar " Iceland Moss," and 

 is alpine or subalpine in its habitat. It grows on the 

 ground on our higher mountains, but is fertile only in 

 the colder regions. 



The thallus is erect and rather stiff, is channeled, 

 with spine-like cilia along the margins. These are 

 so regularly placed that they remind one of the 

 "feet" of a centipede. In color the thallus is a light 

 brown, growing darker at the base or point of at- 

 tachment. Underneath it is almost white, and some- 

 times covered with soredia. 



The apothecia, which are rare, are large and at- 

 tached to the broadened lobes of the thallus. The 

 disk is a dark chestnut, with entire margins. 



Fig. 2. 6. islandica x I. 

 The apothecia are marginal, not common. The disk is chestnut usually 

 with an irregular margin. 



This species is generally found growing on trees, either living or dead ; 

 occasionally it occurs on rocks in an undeveloped form. 



Cetraria Cucui.lata (Bell.) Ach. (Fig. 

 3,) is found in alpine districts, and the 

 mountains of the Eastern and Western 

 States, on the earth, looking very much 

 like a Cladonia. 



The thallus is erect, the edges much 

 rolled, forming a deep channel. The mar- 

 gins are very undulate. It is a light gray 

 green, below it is the same color and very 

 smooth. 



Apothecia are very rare. They are large 

 and adnate to the under side of the 

 curled-over margins. The disk is chestnut 

 with thin entire margin. 



Fig. 3. C. CHcnllafa x 2. 



