LICHENS. 



6i 



In addition to these purplish colorific substances, 

 some of the lichens possess yellow or greenish colour- 

 insr matter, also of an acid nature, such as those due 

 to vulpinic acid, produced in the thallus of Corniai- 

 laria vulpina, and the parietinic acid found in the 

 common wall lichen, Parmelia parietina. Brown 

 colouring matter is also abundantly present in many 

 lichens ; and the domestic woollen hosiery was com- 

 'monly dyed at home in the Highlands with some of 

 the crottles, although they were never sufficiently 

 valuable to be applied commercially on a large scale. 

 One of these was the " Oak-lungs," Sticia pubnonaria, 

 found growing on oak trees (Fig. ii). 



Fig. II. — Oak-Iungs. 



The species of Roccella which constitute the true 

 orchella weed, grows chiefly on maritime rocks, but 

 in some foreign countries it is found on trees, notably 

 on the mango tree in parts of India, It is found 

 very sparingly on the south coast of England, in the 

 Channel Islands, and on the adjacent islands and 

 coasts of France, In tropical Africa, Asia, and 

 America it reaches its highest development, and on 



