1 66 



species are more or less immersed in the thallus. A distinct thalloid 

 exciple exists only in the higher forms. The disk varies from orbicu- 

 lar to irregularly lobate and somewhat folded or crenate ; it is 

 usually flattened, more rarely convex, or its margin slightly raised. 



The, epithecium and upper ends of the simple paraphyses are of 

 the same color as the thallus, that is either dark or yellow. The 

 spore-sacs are long-cylindrical and contain numerous (several 

 hundred, or more) minute, colorless spores. 



The Acarosporas are quite generally distributed, the majority 

 perhaps occurring in the temperate zones ; they grow mostly upon 

 rocks and sandy soil. 



PLATE 42. 



AcAROSPORA. 



i. Natural size. 



2. Single apothecium and fragment of thallus magnified. 



3. Section of apothecium. 



4. Section of thallus. 



5. Paraphyses and spore-sac. 



6. Spores. 



7. Algae, a, as they occur in the thallus; b, normal forms occurring 

 upon the thallus. 



5. Speerschneidera Trev. ; Tuck. Gen. Lich. 17. 1872. 

 This is a somewhat doubtful and little-known genus, so far repre- 

 sented by only one species, S. eufloca. This lichen has certain 

 characters which indicate that it is closely allied to Parmelia, but 

 some authors are inclined to consider it more closely related to 

 Physcia. Many of its characters point to such a double relationship, 

 but, owing to the incongruity of the spore characters, it cannot be 

 included in the Physciaceae. 



The thallus is foliose, with a slight fruticose tendency. It is 

 uniformly and frequently dichotomously branched ; the lobes are 

 narrow, linear and of uniform width throughout. The appearance 

 -of the thallus is so characteristic that it cannot readily be mistaken ; 

 its color is light grey above and below ; the lobes are more or less 

 curved upward, so that they only come in contact with the substra- 

 tum at certain areas, at which the rhizoids occur. 



Upon microscopical examination of the thallus it is found that the 

 upper and lower cortical layers are enormously developed, while the 



