Knowles — The Maritime and Marine Lichens of Howth. 97 



the close mat of its thallus. On the shady rocks on the shore at Glenaveena 

 and at several other places Parmelia proUxa is very abundant, covering large 

 areas on the landward faces of the rocks and on the top growing witli 

 Physcia aquila and Lecanora parella, and pushing its way in amongst the 

 tufts of RamaUna scopulorum. On the moister and more sliady faces of the 

 rocks lying along the foot of tlie cliffs the isidiose form grows with the 

 species. Tliis form was also noted in several places on the eastern coast. 

 Parmelia prolixa is partial to quartz rocks, but it also occurs on the shales ; 

 and, though it seems to prefer rather smooth and flat or slightly sloping 

 rocks, it sometimes grows on steep shady surfaces. 



Parmelia conspersa and Parmelia fuUginosa grow at higher levels than 

 P. prolixa. On the south-west coast they are usually associated with RamaUna B. 

 Amongst the Ramalinas of the lower cliffs they grow as isolated patches and 

 are of so rare occurrence that they can hardly be described as forming part 

 of the subvegetation at these levels. 



The way in which these two species cover the bare rocky tracts of the 

 western and higher slopes of the hill above Red Rocks has been referred to 

 already on page 92, and may be taken as typical of the mode of growth all 

 over the headland. Parmelia conspersa occupies large areas on the flat rocks 

 that lie level with the soil and on the sides and bottoms of the shallow 

 channels over which the surface-water runs. 



Parmelia fuUginosa is more usual on the rather steeper surfaces, but the 

 two species frequently grow together. The pale yellowish-green circular 

 growths of P. co)'.spersa are always fertile, and with the dark-brown velvety 

 thallus of the less abundant P. fuUginosa make a beautiful piece of colour 

 against the background of the reddish quartzites. Parmelia Mougeotii is 

 occasionally associated with them near the top of the hill and somewhat 

 resembles P. conspersa ; but it is easily distinguished by the more finely 

 divided thallus, tlie darker central area of which is covered with little 

 pale yellow sorediate dots. 



Parmelia omphalodes and P. saxatilis are very scarce inside the Ramalina 

 area on the south-west coast, but are of general occurrence on the east 

 and northern coasts, and are sometimes found a good way down the cliffs on 

 bare places amongst the Ramalina tufts. Parmelia perlata and sub-species 

 ciliata are also frequent on the east coast. 



Parmelia physocles is abundant on the headland, growing on the rocks and 

 on Heather stems and on the Blackthorn shrubs. The sorediate form labrosa 

 is more general than the species; but both are to be seen on bare rocks 

 amongst the sparser growths of the upper Ramalinas all round the coast. 

 The species is most abundant on the north coast, but is not often encountered 



p 2 



