532 MANUAL OF NATURAL HISTORY. 



II CLASS.— THALLOGENS (Thallogenas). 



Entirely cellular; stems and leaves undistin- 

 guishable ; stomata none ; reproduction by spores. 



I. OEDEE. — 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 oiLecanora; Litmus, 

 from various Roccellce and Variolarice; 

 others afford nutritive matter, as Iceland- 

 Moss (Cetraria Lslandica), and some species 

 of Sticta, also Gladonia rangiferina, or 

 Eein deer-Moss. 



2. Family. — Glutinous - Lichens (Collemacese). 



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 Eoche/' is occasionally the 

 principal subsistence of northern hunters 

 and Arctic travellers. 



