ERRATIC LICHENS 



259 



bind the mass together. Meyer says that " wanderers " have been noted as 



belonging to Parmelia acetabulum, Platysmaglaucum and Anaptychia ciliaris. 



The most notable instance in Britain of the "erratic" habit is that of 



Parmelia revoluta y-ax. concentrica (Fig. 121), first found on Melbury Hill 





■ - ^ V 









ft;/i«.>x^:^ 





iM^MrM.. 







^K 



.5; •>i'^ 





%' 



^l^SlSSS^i 





:H,' 



Fig. 131. Parmelia revoluia var. concentrica Cromb. a, plant on flint with detached fragment; 

 b, upper surface of three specimens ; <r, three specimens as found on chalk downs ; d, specimens 

 in section showing central cavity (S. H., Photo.). 



17—2 



