THE LICHENS 417 
lichens, such as Cetraria islandica, various species of Parmelia, 
Usnea and Alectoria, have been used in medicine because of 
demulcent principles which they contain. 
One of the most conspicuous lichens in northern latitudes is 
the Reindeer Moss (Cladonia rangiferina). It is a slender, 
branched, fruticose form which grows to the height of about a 
foot and bears its brownish apothecia at the ends of branches. 
In Arctic regions it occurs in dense patches covering large areas 
and forms the only kind of fodder available in many sections for 
reindeer and caribou. 
Another lichen, Lecanora esculenta, is thought to represent the 
source of Scriptural Manna. It has been employed as a food in 
periods of famine by the natives of southwestern Asia. 
