XI 



and the bark with the genera Tkelotrema, Verrucaria, Trypethelium, 

 CModecton, Graphis, &o. The Graphidece which abound in this 

 and the temperate, zone diminish in number and profusion as the 

 arctic zone is approached. Certain species, especially the saxicolar 

 ones, are cosmopolitan. -Our British Lichen-Flora may be taken 

 as a fair representative of the liohens of the Temperate Zone. 



If we particularise the several Tribes their distribution may be 

 shewn more clearly, thus : — 



Byssaoei ; entirely in Temperate zone. 



Liohinei; Temperate. 



Collbmei ; Temperate, very few Tropical, 



Myriangiei ; Temperate, Arctic and Tropical. 



Calioiei ; Temperate, few Tropical. 



SpHiEKOFHOREi ; Temperate, very few Tropical. 



BiEOMTOEi ; Temperate and Tropical. 



Cladoniei ; Arctic, Temperate, decreasing towards Tropics. 



Stereooaulei ; Temperate and Arctic, especially decreasing 

 towards Tropics. 



Rocoellei ; Temperate and Tropical. 



Siphulei ; Temperate and Tropical. 



Usneei ; Cosmopolitan. 

 ■ Ramalinei } Cosmopolitan. 



Cetrariei ; Arctic, Temperate, few in Tropics. 



Peltigerei ; Temperate, Arctic, few in Tropics. 



Paemeliei ; Temperate, Arctic, decreasing in number in Tropics, 

 but there attaining maximum development in the Stictei. 



Gybophorei ; Arctic, Temperate, decreasing towards Tropics. 



Lecanorei ; chiefly Temperate, Arctic numerous, and Tropics. 



Lecideinei ; chiefly Temperate, numerous in Arctic and 

 Tropical. 



Gbaphidei ; chiefly Temperate, few Arctic, numerous Tropical. 



Peridiei; Temperate. 



Pyrenocarpei : chiefly Temperate, Arctic many, Tropics com- 

 paratively less numerous. 



Their variation in altitude is also very great, as may be readily 

 observed in the ascent of lofty hills and mountains, the lichens 

 of the plains occurring at the bases and lower altitudes, and the 

 subalpine lichens making their appearances as one ascends upwards 

 to the very summit. Nevertheless Cetraria Islandica and Getraria 

 aculeata occur plentifully, the latter in fructification, on North 

 Wootton Heath, Norfolk, and in Lincolnshire only 200 feet 

 above the level of the sea, probably brought there in a glacial sera 

 and surviving on the retreat of the glacier. On the other hand 

 Sir J. D. Hooker observed Placodium miniatum with Physcia 

 flavicans on the Himalayan mountains, on the very summit of 

 Bhomtso, alt. 18,590 feet. The former Placodium miniatum 

 is the most Arctic, Antarctic, and Alpine lichen in the world, 

 colouring the rocks of an orange-red, as at Bhomptso, and on 

 Cockburn Island in the Antarctic Ocean, Thamnolia vermicularis, 



