410 INTRODUCirON TO CllYPTOGAMlG BOTANY. 



the discs are extremely small and obscure. One of the most 

 beautiful forms is presented by the antarctic Cenomyce reticu- 

 lata (Fig. 19), the podetia of \^hich are elegantly reticulated, 

 the meshes being traversed by delicate fibres so as to present 

 the most charming effect. The discs, as in most cases where 

 the thallus is so highly developed, are small and unattractive. 

 Stereocaulon replaces Cladonia on exposed rocks, though the 

 latter genus is by no means completely excluded any more 

 than Stereocaulon is confined strictly to rocks. The podetia 

 are here again strongly developed, and rough with minute 

 processes ; and the apothecia have a distinct margin without 

 that constant tendency to become distorted, which is so com- 

 mon in Cladonia. 



446. Some of the minuter forms occur on tropical leaves, 

 resembling closely certain species of Stictis. One of the most 

 curious of these is Sporopodium * (Fig. 87, a), in consequence of 

 the size of the single sporidium, which is formed from the upper 

 part only of the protoplasm of the asci, the lower part remain- 

 ing barren, and forming, as it were, a little peduncle to the 

 sporidium, in the style of the Phasnogamous PodosperniuTri. 

 Some of the exotic epiphyllous Lichens, consisting of a thin 

 crust and upright threads, referred to two or three genera by 

 F^e, as Melanoplaca, appear so abnormal, that I am inclined 

 to consider them as imperfect or altered conditions of other 

 Lichens. Septate conidia have been found in at least one 

 species, but this is not inconsistent with the view just stated. 

 It remains to notice here the genus Ccenogonium, which is 

 allied to Biatora, though differing so greatly in the floccose 

 tissue, the cortical being entirely suppressed. I am the rather 

 inclined to think that its true affinities are here, because I 

 possess a production, gathered in Switzerland, consisting of the 

 apothecia of Biatora, and a cnist composed of erect threads 

 like those of Chroolepus, a confirmation of my notion that 

 that genus, like Gephcdeurus, may be a mere anamorphosis of 

 the crust of Lichens. The genera are for the most part 

 ubiquitous, as are a great many of the species also. Lecidea 



* ]\Iont. in Ann. d. Sc. Nat., scr. 3, vol. 16, p. 54. 



