'59 



The apothecia are of medium size and are quite common on 

 most species, especially so in T. polycarpus, but they are rare or 

 wanting in T. jl&vicans . The formation of soredia is less common 

 than in Physcia. In the higher fruticose forms the apothecia are 

 usually terminal, a character which also manifests itself in the fruti- 

 cose Physcias. In the lower fruticose forms and the foliose forms 

 the apothecia may be terminal, on the margin or upon the surface. 

 The disk is yellow or orange in color ; the margin of the cup is 

 frequently lined with cilia. In other respects the apothecia resemble 

 those of Physcia and Placodiitni. 



The spores closely resemble those of Placodinm, which seems to 

 be strong evidence that this group is phylogenetically derived from 

 that genus. 



In their distribution the Theloschistes are still more southern than 

 the Physcias, and they also have a western range. They occur upon 

 the bark and smaller branches of trees, rarely upon decaying wood, 

 old boards, rocks, etc., frequently in association with species of 

 Physcia. 



PLATE 38. 



THELOSCHISTES CHRYSOPHTHALMUS (L.) Norm. 



1. Natural size. 



2. Terminal portion of thallus magnified. 



3. Section of apothecium. 



4. Longitudinal section of thallus. 



5. Paraphyses and spore-sac with spores. 



6. Spores. 



Family 6. PARMELIACEAE. 



The limitations and position of this family are dependent upon four 

 essential characters, i. The presence of the thalloid exciple sepa- 

 rates it from the Caliciaceae, Cladoniaceae and Lecidiaceae. 2. The 

 non-union of the spore-plasms excludes it from the Physciaceae. 

 3. The presence of the discoid apothecium separates it from the 

 Verrucariaceae. 4. The absence of cyanophyceous algae separates 

 it from the Collemaceae and Pannariaceae. It has more nearly the 

 general characters of the Lecideaceae than any other family, those 

 of the apothecia being very much alike. 



In this group the fruticose thallus reaches its highest develop- 



