532 MANUAL OF NATURAL HISTORY. 



II. CLASS. THALLOGENS (Thallogense). 



Entirely cellular ; stems and leaves undistin- 

 guishable ; stomata none ; reproduction by spores. 



I. ORDER. LICHENALS {Lichenales). 



Live in air ; nourished through their whole 

 surface by the medium in which they vegetate ; 

 propagate by spores, which are usually enclosed in 

 asci, and have always green gonidia in their 

 thallus. 



1. FAMILY. Scutiform - Lichens (Parmeliacese). 



Nucleus bearing asci ; thallus heterogeneous., 

 pulverulent, or cellular. Several yield dyes, 

 as Cudbear, from species ofLecanora; Litmus, 

 from various Roccellce and Variolarice; 

 others afford nutritive matter, as Iceland- 

 Moss (Cetraria Islandica), and some species 

 of Sticta, also Cladonia rangiferina, or 

 Eein deer-Moss. 



2. FAMILY. Glutinous - Lichens (CollemaceaB). 



Nucleus bearing asci ; thallus homogeneous, 

 gelatinous, or cartilaginous. 



3. FAMILY. Graphic-Lichens (Graphidacese). Nu- 



cleus breaking up into naked spores ; 

 apothecia resembling Oriental characters. 

 Some kinds supply a scanty nutriment, as 

 species of Gyrophora, which, under the name 

 of "Tripe de Roche/' is occasionally the 

 principal subsistence of northern hunters 

 and Arctic travellers. 



