The Scottish Naturalist. 



23 



P. physodes is the most abundant of all lichens on pine-trees and 

 rocks, and P. pertusa, which is closely allied to it in appearance > 

 is one of the rarest ; in New Zealand on the other hand P. pertusa 

 takes the place of our P. physodes, and is the commonest 

 arboreal species in the country. So with Ricasolia amplissima ; 

 in eastern and central Scotland it is almost unknown ; while 

 in the neighbourhood of Inveraray it is, as I have said, the 

 commonest lichen. What is it that determines this strange 

 geographical distribution of lichens? It may be difficult to 

 account for the localisation of some species ; but there can be no 

 difficulty about the Ricasolia in question. It is obviously a lichen 

 that requires a very moist mild climate, and dense shady woods, 

 where the air is little disturbed. These conditions are to be 

 found at Inveraray as they are to be met with in scarce any 

 other locality in Scotland. 



Associated with this magnificent lichen is another scarcely less 

 magnificent, belonging to the same genus, the Ricasolia 

 laetevirens. This species is destitute of the curious glomules 

 that characterise the sister-species ; its texture is thinner and less 

 coriaceous ; its lobes are less scolloped ; and, though of the same 

 rich green colour when wet, it is of a brownish colour when dry. 

 It grows in equal abundance and luxuriance at Inveraray ; and 

 though not nearly so rare in Scotland as R. amplissima, it is in 

 this locality more frequent and attains a larger size than elsewhere. 

 It often occurs on rocks, trees, and banks on the seashore ; and it 

 seems to require for its well-being a touch of saltness in the air. 



The Stictinas and Stictas, belonging to the same sub-tribe 

 (Stictei) as the Ricasolia?, also abound in the woods of Inveraray. 

 Almost all the British species grow in this locality ; and they 

 flourish here more abundantly than in most other places which they 

 affect. Almost all the trees are shaggy with the loose hanging re- 

 ticulated lobes of Sticta pulmonaria or " Lungwort ; " and 

 specimens of it in fructification are by no means infrequent. 

 Stictina SCrobiculata is not quite so abundant or luxuriant ; 

 but yet it attains fair proportions, and often mingles its grey mealy 

 rounded lobes, which strangely change to a dull leaden colour 

 when wet, with its commoner and more ragged congener. The 

 fructification of this species is exceedingly rare. I have examined 

 myriads of specimens ; but have found them all barren. I ob- 

 tained several fronds with the characteristic apothecia on them at 



