i5i 



This group, of which there are only a few representatives, is 

 somewhat southern in range. The species occur upon trees, most 

 frequently upon the hickories. 



PLATE 33. 

 Arthothelium spectabile (Fw.) Stein. 



1. Natural size. 



2. Portion magnified. 



3. Section of apothecium. 



4. Section of thallus. 



a, epiphloeodal portion ; b, c, d, hypophloeodal portion. 



5. Paraphysis and spore-sac. 



6. Spores. 



Family 5. PHYSCIACEAE. 



This family again forms a well-determined and natural group. 

 Its representatives are at once recognized by the spore-characters. 

 The spores are two-celled, the two terminal or nearly terminal plas- 

 mic masses are united by a plasmic thread, which character does not 

 exist in any other lichen group. In Rinodina oreina this plasmic 

 connection is often not noticeable. In fact, it seems to occur so 

 rarely that I was at first inclined to exclude this plant from the genus. 

 The plasmic connection was, however, quite evident in a number of 

 spores ; besides, the general characters of the species indicate that it 

 is closely related to Rinodina. It may also be mentioned that various 

 authors have placed R. oreina in the genus Dimelaena, which is 

 supposed to be characterized by "immersed apothecia." A care- 

 ful comparative study of the representatives of the genus Rinodina 

 soon demonstrates that the apothecia are more or less immersed in 

 the thallus in all of its lower species. 



Referring to the key (p. 10) it will be seen that this is the first 

 family in which the thalloid exciple becomes apparent ; it is unmis- 

 takable in Theloschistes, Physcia and Pyxine, but in Rinodina and 

 Placodium it is sometimes not very apparent, especially in those 

 forms in which the apothecia are mostly immersed. In nearly all 

 cases a close examination with a lens will reveal the thalloid outer 

 covering of the apothecium which usually extends slightly above the 

 margin of the dark disk. 



The generic characters are sufficiently marked, so that it will not 

 be necessary to give any lengthy description of the family characters. 



