158 



PLATE 37. 



PHYSCIA SPECIOSA Fr. 



1. Natural size. 



2. Section of apothecium. 



a, thecium ; b, c, the two layers of the hypothecium ; d, upper algal 

 layer ; e, medullary layer ; f , lower algal layer ; g, cortical layer. 



3. Section of thallus. 



a, colored layer; b, cortical layer; c, algal layer; d, medullary 

 layer ; e, lower cortical layer. 



4. Paraphyses and spore-sac with spores. 

 ^. Spores. 



6. Colorless spores of another species. 



7. Algae. 



5. THELOSCHISTES Norm. ; Tuck. Gen. Lich. 18. 1872. 



The question whether Theloschistes or Physcia is the higher seems 

 to me undecided. As previously indicated the fruticose forms repre- 

 sent the climax of structural development ; the fruticose tendency is 

 more marked in this genus, for which reason I consider it the higher, 

 but the plausible objection that the development of Theloschistes as a 

 whole is lower than Physcia can, however, be raised. 



The representatives of this genus are recognized by the presence 

 of a yellow or even orange coloration in the thallus and apothecia, 

 and the fruticose tendency of the thallus. T. parietinus is, however, 

 distinctly foliose, although the lobes have a tendency to ascend or to 

 turn upward at the margin. The extreme fruticose development is 

 reached in T. flavicans, in which species the thallus-branches are very 

 long, linear, somewhat rounded, showing a marked tendency toward 

 a radial structure. In the majority of species the thallus-lobes are 

 distinctly flattened (centric structure) and comparatively short. In 

 some species the thallus is very short, the lobes are flat and sparingly 

 branched toward the top {T. poly carpus}. The thallus is attached 

 to the substratum by clusters of root-like rhizoids. In the foliose 

 forms the bunches of rhizoids occur toward the middle portion of the 

 thallus ; cilia also occur on the margin of the lobes and apothecia. 



The yellow color of the thallus is due to a deposit of crystals of 

 chrysophanic acid, as m Placodiiuu, which occurs most plentifully on 

 the upper surface of the younger portions, gradually fading into grey 

 or brown with age. The lower surface is usually pale yellow or 

 grey, likewise showing a shading in color similar to the upper. Black 

 coloration is wanting ; the rhizoids are usually grey. 



