20 FIRST STEPS IN GENERAL KNOWLEDGE. 



to be poisonous to wolves. Chemists tell us that 

 lichens contain several peculiar bitter principles 



" LTINGS OF THE OAK " LICHEN. 



and colouring matters ; and many of the species 

 are rich in a substance called usnine, or usnic acid, 

 which is of a yellow colour, but changes by expo- 

 sure to the air, and by its various combinations 

 produces many of the beautiful colours observed in 

 lichens." 



"And some of those are the colours used in 

 dyeing, I suppose," said Henry. 



" The chief supply of dyeing-material is obtained 

 from a white or grayish lichen, growing abun- 



