LICHEN COMMUNITIES 



387 



above the tidal line and Lecanora galactina does not descend below tidal 

 limits ; the latter is an arenicolous species and colonizes some of the loosest 

 and sandiest areas of shingle. Rhizocarpon confervoides is ubiquitous. 



c. MOUNTAIN LICHENS. On the mountain summits of our own and 

 other lands are to be found lichens very similar to those of the far North 

 the- climatic conditions being the chief factors of importance in determining 

 the formations. These regions are occupied by what Wheldon and Wilson 1 

 describe as " a zone of Arctic-Alpine vegetation," and they have recorded 

 a series of lichen associations belonging to that zone on the schistose 

 summits of the Perthshire mountains. The following is one of the most 

 typical : 



Euopsis granatina. 

 Sphaerophorus coralloides. 

 Sphaerophorus fragilis. 

 Gyrophora polyphylla. 

 Cetraria tristis. 

 Cetraria nivalis. 

 Lecanora tartarea var.frigida. 

 Lecanora upsaliensis. 

 Aspicilia oculata. 

 Pertusaria dactylina. 

 Pertusaria glomerata. 

 Stereocaulon denudatum. 



Parmelia saxatilis. 

 Parmelia omphalodes. 

 Parmelia lanata. 

 Parmelia stygia. 

 Stereocaulon tomentosum. 

 Stereocaulon alpinum. 

 Cladonia coccinea. 

 Cladonia gracilis. 

 Cladonia uncialis. 

 Cladonia destricta. 

 Cladonia racemosa. 

 Lecidea arctica. 



Parmelia alpicola. 

 Cetraria aculeata. 

 Cetraria crispa. 

 Cetraria islandica, 

 Lecidea limosa. 

 Lecidea alpestris. 

 Lecidea demissa. 

 Lecidea uliginosa. 

 Lecidea cuprea. 

 Lecidea Berengeriana. 

 Lecidea cupreiformis. 

 Lecidea atrofusca. 



Again on the summit of Ben-y-Gloe the same authors 2 have recorded 

 " Gyrophora erosa, G. torrefacta and G. cylindrica, Parmelia alpicola, Lecanora 

 tartarea var. frigida, Lecidea limosa and L. arctica, the last two lichens 

 thriving in the most bleak and exposed situations. Cladonia cervicornis 

 grew in reduced squamulose cushions ; Stereocaulon and Sphaerophorus in 

 very compact forms, the outer stalks prostrate, the next inclined, the central 

 ones erect so that points only are exposed and no lateral stress is caused by 

 wind storms. Erect fruticose lichens are absent in this region, being repre- 

 sented only by Parmelia lanata, a semi-decumbent plant, and by Thamnolia 

 vermicularis which is prostrate on the ground except where the points of 

 the stalks turn up to catch the dew. Many of the Lecideae were observed to 

 have large fruits and very little thallus : " the hyphae ramify in the minute 

 interstices of the stone and the gonidia cluster under the lea of the apothecia; 

 this is especially the case on loose stones where conditions are extremely 

 dry." 



On the Continent an interesting study of the lichens of high altitudes 

 was made by Maheu 3 in the Savoyard Oberland. On the Great Casse at 



1 Wheldon and Wilson 1915. 



2 Wheldon and Wilson 1914. 



3 Maheu 1887. 

 252 



