LICHENS. 125 
universal diffusion of lichens, being the most 
Arctic, Antarctic, and Alpine lichen in the world 
—facing the savage cliffs of Melville Island in 
the extreme north, clinging to the volcanic rocks 
of Deception Island in the extreme south, and 
scaling the towering peak of Kinchin-junga, the 
most elevated spot on the surface of the earth, A 
catholic beauty, it is to be found in every zone of 
altitude and latitude—‘a pilgrim bold in Nature’s 
care. 
On the British mountains we find lichens in 
great abundance and luxuriance, in spots which 
favour their growth by the humidity continually 
precipitated from the atmosphere. Most of the 
species found sparingly scattered at the highest 
elevations are identical with those found in the 
greatest profusion covering immense areas on the 
plains of Lapland, and on the level of the sea- 
shore in the Arctic regions ; the isotherms or lines 
of equal temperature passing through these points. 
Similar species are also found all over the world 
below the level of perpetual snow, which on the 
Alps is 7000 feet, and on the Andes and Hima- 
layas about 15,000 feet. It is somewhat remark- 
able that Alpine lichens generally are more or less 
ofa brown or black colour. This peculiarity seems 
to be owing to the presence of usnine or usnic 
acid, which in a pure state is of a green colour, 
