GEOGRAPHICAL DISTRIBUTION. 



105 



tusaria communis ; others are common in ^ubalpine districts, 

 on hills of minor elevation, as Lecanora tartar ea and veii- 

 tosa, Cladonia rangiferina, Cetraria Islandica and aculeata ; 

 while a few are essentially alpine, and characteristic of the 

 summits of our highest mountains, as the Umbilicarias, 

 some Cladonias and Lecideas, Peltigera venom, Parmelia 

 Fahlunensis, and others. There, luxuriating in the moisture 

 of the dense mists in which they are almost constantly 

 bathed, many species attain a high state of development, 

 and some of them, great beauty, as the Solorina crocea ; of 

 this any tourist may convince himself by clambering to the 

 summit of Ben Lomond or Ben Nevis. While certain spe- 

 cies are found chiefly or solely on trees, rocks, or the ground, 

 others, under different circumstances of locality or climate, 

 may be indiscriminately corticolous, saxicolous, or terrico- 

 lous ; or species which inhabit rocks in one country or climate 

 may be found on trees in another. With such changes 

 in the nature of the habitat, however, it is but reasonable 

 to expect corresponding alterations in the characters of the 

 plants : hence we frequently find the fructification altered, 

 — a Lichen which is fertile when growing on a tree becoming 

 sterile on a rock, or vice versa. 



Bibliography : — Hooker, Dr. J. D., Flora Antarctica, Cryptogamia Ant- 



