382 



ECOLOGY 



Parmelia prolixa is the most abundant of the Parmelias : it covers large 

 spaces of the rocks and frequently competes for room with the Ramalinas, 

 or in other areas with Physcia aquila and Lecanora parella. 



A number of crustaceous species which form the sub-vegetation of the 

 Ramalina belt, and also on the same level, clothe the steeper rock faces 

 where shelter and moisture are insufficient to support the foliose forms. 

 "In general the sub-vegetation of the eastern and northern coasts is largely 

 composed of species that are common in Alpine and upland regions. This 



Fig. 



125. Crustaceous communities in the Ramalina belt. Lecanora atra Ach. (grey patches) and 

 Buellia ryssolea A. L. Sm. (dark patches). (After M. C. Knowles, R. Welch, Photo.) 



is due to the steepness of the rocks and also to the colder and drier conditions 

 prevailing on these coasts." An association of Rhizocarpon geographicum, 

 Lecanora {sordida) glaucoma and Pertusaria concreta f. Westringii forms an 

 almost continuous covering in some places, descending nearly to sea-level. 



On sunnier and moister rocks with a south and south-west aspect the 

 association is of more lowland forms such as Buellia colludens, B. stellulata 

 Lecanora smaragdula and L. sivtplex f strepsodina. 



(2) The Orange belt. "Below the Ramalinas, and between them and 

 the sea, several deep yellow or orange-coloured lichens form a belt of varying 



