254 LICHENS 



asks and receives nothing from its host but standing 

 room, drawing all its nutrition from the sun and rain of 

 heaven. This is specially interesting in connection with 

 the chemical properties and economic uses of lichens. 

 One is so accustomed to think — of course wrongly — that 

 vascular plants, the green things of the earth, extract 

 and distil their various properties only from the soil 

 wherein they are rooted, that it surprises one to find 

 that such primitive cellular plants as lichens, which 

 possess no means of deriving nourishment except from 

 the air and light and rain, contain such unexpected 

 substances as iron, salt, sugar, oil, resin, starch, and a 

 whole host of chemical agents. The Highlanders who 

 scrape the crottle and ' staneraw ' from the rocks to dye 

 their yarn withal, are pursuing a very ancient industry ; 

 for society was in a very unfinished state when various 

 kinds of lichens were made to yield their secret virtue 

 of producing rich dyes in reaction to ammonia — scarlet, 

 purple, yellow, russet, and green. Litmus, commonly 

 used by chemists for the detection of free acids and 

 alkalies, is extracted solely from species of Bocella and 

 Lecanora. Arctic travellers nowadays carry their own 

 provender with them, cunningly preserved; but the 

 pioneers in high latitudes sometimes owed their lives to 

 'Iceland moss' and tripe de roche, ground to powder 

 and baked in cakes. All these lichens are attached to 

 rock or soil, and some people may feel sceptical about 

 the assurance of men of science that they draw nothing 

 from that on which they grow; but the most nutritive 

 lichen of all is above suspicion, for it grows detached 

 from any foothold. This is the manna lichen {Lecanora 

 esculenta), which lies in loose lumps or cakes, several 



