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POPULAR HISTORY OF LICHENS. 



Nat. Ord. III. CETRARIA CEJE. 



Fam. Char. Thallus foliaceous or sub-fistulose, prostrate, as- 

 cending or erect, cartilaginous or membranaceous, generally reti- 

 culate-lacunose. Apothecium peltate, affixed obliquely and ante- 

 riorly to the apices of thalline lobules. 



The Cetrarias may be considered intermediate between 

 Lichens having a fruticulose, ascending thallus, and those 

 having a foliaceous, horizontal one : hence the sub-fistulose 

 thallus, which is somewhat analogous to the hollow po- 

 detium, approximates a certain section to the Cladonice, as 

 C. Islandica, C. aculeata, and C. nivalis; while certain 

 others, such as C. glauca and C. juniperina, closely resem- 

 ble the Parmelias in the nature of their vegetative system. 



Genus I. CETRARIA, AcL 



Name derived from KaiTpea, cetra or ccetra, an ancient 

 shield of a peculiar form, which the apothecia are supposed 

 to resemble. 



1. Cetraria glauca (glaucus, greyish-blue). Thallus 

 foliaceous, membranaceous, prostrate, — above glaucous, 

 slightly reticulate-lacunose, — below brownish-black or va- 

 riegated with white, smooth, — sinuate-laciniate ; fertile la- 

 cinise ascending; apothecia dark brownish-red, terminal. 



