304 USNE.E. PART IT. 



posing the light, and adorning themselves in brilliant 

 hues. In our own country, where the colouring is often 

 cold from the excess of verdure, the lichen affords a happy 

 relief by giving a little warmth to the landscape. Even 

 at Rome, where nature is so gorgeously coloured, the 

 ruins owe much of their picturesque beauty to the 

 red, white, and golden lichens with which they are 

 clothed. 



The Usnese are perhaps the most beautiful of the 

 lichens, the colours being sometimes brilliant, the forms 

 elegant, and when the broad discs are amply ciliated, 

 the appearance is very striking. The same species 

 are widely diffused, but the colours are brighter in exotic 

 specimens. Usnea melaxantha and Usnea Taylori are 

 splendid productions. 8 The Usnese are cosmopolitan 

 in genera and species. The genus Cetraria, of which 

 the Iceland moss is a well known species, forms a 

 connection between the vertical and horizontal lichens ; 

 its thallus is neither cylindrical nor quite erect, though 

 it becomes more so towards maturity. The Cetraria 

 tristis has only that degree of inclination which arises 

 from its crowded mode of growth, and springs like a 

 sea- weed from a little peltate disc. 



The most typical species of lichens occur in the 

 second group of Euparmeliacese, or Parmeliacei proper, 

 in which the disc is at first closed, and surrounded after 

 expansion by a border arising from the thallus or frond. 

 The thallus is always horizontal, and expands from the 

 centre towards the circumference. The genus Sticta, 

 belonging to this group, is often highly foliaceous, and 

 is not excelled by any horizontal lichen in brightness of 

 colouring or elegance of form. Even in our own country 

 the Sticta pulmonacea spreads over a wide area, and is 

 remarkable for its pitted frond. In this genus the under- 

 side of the plant is covered with a delicate velvety 



8 Berkeley's ' Introduction to Cryptogamic Botany.' 



