100 



POPULAR HISTORY OE LICHENS. 



are replaced by Stictas, which again are rare in Arctic islands 

 or continents. Tuckerman mentions the absence of Physcia 

 prunastri, a very common British species, from North Ame- 

 rica ; and Dr. Hooker notices the scarcity in the Southern 

 Hemisphere of some species which are common in the 

 northern, and the abundance of some in the southern ex- 

 treme of the Western Hemisphere, which are entirely absent 

 from a similar position in the Eastern. Certain species 

 again are peculiar to the Antarctic regions, such as the 

 SpJuerojphoron australe, which is confined in its geographi- 

 cal range to the Straits of Magellan. 



On the highest mountains, between the region of shrubby 

 alpine plants and the snow-line, or between an elevation of 

 13,000 and 16,000 feet, there is a terminal zone of vegeta- 

 tion, denominated the region or zone of Lichens. In regard 

 to vertical range on a tropical mountain, the Lichens may 

 therefore be said to form the base as well as the apex of a 

 cone, whose sides may be considered as covered with every 

 tribe of the vegetable kingdom, from the proudest of the 

 Palm family to the tiniest Moss. On the central and south- 

 ern Alps the highest limit of phanerogamic plants occurs at 

 an elevation of about 10,000 Paris feet. But species of Par- 

 melia, Lecidea, and Umbilicaria are found on all the rocks 



