92 



Mycologia 



Protective Coloration 



A remarkable thing about these rock-inhabiting lichens from 

 Tumamoc Hill is the more or less evident development of black 

 lines or spots on the upper surface of every species having a 

 light-colored thallus. These lichens or spots are so numerous on 

 older portions of some of the thalli as to darken, more or less, 

 the otherwise light-colored surface. The lines are most con- 

 spicuously developed on some of the thalli of Acarospora xan- 

 thophana and Parmelia conspersa, and it was at first thought that 

 they represented parasitic fungi, but sectioning showed that they 

 do not. Zukal, in his excellent discussion of the protective sig- 

 nificance of colors in lichens, speaks of such lines of black as 

 occurring on younger or injured portions of thalli to protect the 

 algal cells from the intense rays of sunlight in hot regions;* but 

 the writer found the lines and spots better developed over older 

 portions of thalli and noted that they were frequently developed 

 in connection with cracks in the thalli; nor were the algal cells 

 any more numerous, so far as could be determined, under these 

 black areas than elsewhere in the same thalli. Parmelia con- 

 spersa, Acarospora xanthophana and Lecanora muralis all showed 

 more or less of black margins, which doubtless protect the younger 

 and more tender algal cells of these margins where the cortex is 

 still thin. It was thought that in some of the areolate forms as 

 Buellia lepidastra and Acarospora xanthophana, in which the 

 thallus is compound, each areole really representing an indepen- 

 dent development, the black lines might have been developed at 

 first along the margins and become dorsal by subsequent growth 

 of the areole ; but, were this the case, the lines would be as 

 numerous on younger as on older portions of thalli. Besides the 

 species mentioned above, these lines and spots were readily noted 

 in Acarospora xanthophana dealbata, Acarospora cineracea, Le- 

 canora cinerea and Lecanora calcarea contorta. In section, under 

 the microscope, the upper surface of older portions of some thalli 

 showed the coloring matter often quite generally distributed; 

 whereas under the hand lens it was only apparent where best 

 developed as the black lines or spots, the protective coloration 



* Zukal, H. Op. c. 218-221. Mr 1896. 



