198 



POPULAR HISTORY OF LICHENS. 



implies, on rocks and stones, but also on trees, in lowland, 

 subalpine, and alpine districts. Like the preceding, however, 

 it is rare in fructification ; in this neighbourhood we have 

 met with it fertile on trees near Pitkaithly Wells, and on 

 granitoid rocks and boulders on Birnam Hill, Dunkeld. It 

 appears to be more frequently fertile in highland than low- 

 land districts ; we have found it abundantly so on Ben Lo- 

 mond and the neighbouring mountains. In its most common 

 form, in lowland districts, the lacinise are broarlish, deeply 

 reticulate-lacunose, with somewhat naked margins, smooth 

 or covered with a pulverulent, furfuraceous or isidioid efflo- 

 rescence. A saxicolous variety (var. omphalodes) , peculiar 

 to subalpine and alpine districts, has a smoothish, shining, 

 bronze-coloured th alius, w T ith broadish, slightly reticulate- 

 lacunose lacinise, having sometimes black-ciliate margins : 

 this is the Parmelia omphalodes of older authors ; it is com- 

 mon on boulders and rocks on all our Highland mountains. 

 We have found these varieties passing insensibly into each 

 other, especially in respect to colour. The latter variety is 

 probably more frequently fertile; its apothecia are larger, 

 more irregular in form, sometimes confluent, and usually 

 have a crenate margin ; its spores, in the specimens we have 

 examined, are oval or ellipsoid, simple, of medium size, pale- 

 yellow and double-walled. 



