Knowles — The Maritime and Marine Lichens of Howth. 103 



shelter, and a greenish grey orustaceous lichen (Lecaiiora prosechoides) has 

 intruded itself between the Plaoodiiims and the Eamalinas, covering the 

 steeper sea-faces of the rocks, and especially those with an easterly or south- 

 easterly aspect, with a close and continuous crust. As the sliore curves back 

 again into slielter to form the bay west of Lion's Head (Stella Maris), Lecanora 

 prosechoides sinks out of siglit amongst the Placodiums, and Physcia parietina 

 emerges from under tlie Ramalinas to occupy its normal position in the 

 upper part of the Orange Belt. The same variations may be traced on 

 the cliffs. On sheltered and gently sloping faces Physcia parietina and 

 the Placodiums form two more or less distinct parallel bands overlapping 

 in the middle. But where the surface is steeper and v?here the seas are 

 rougher and there is rather more dash of water, Physcia parietina and 

 Placodium tmiroricm seem to disappear, leaving Placodimn lobulatum the sole 

 representative of the orange lichens, while' Lecanora prosechoides at once 

 makes its appearance above it as a greyish band, varying in width from 

 3 to 6 feet according to slope and exposure. Where Placodium lolulatum and 

 the Lecanora meet tlie rock-surface is variegated with spots of grey and 

 orange. On the steep quartzites of the Needles and at other places round 

 the coast, the band of L. jjrosechoides is also frequently interspersed with 

 spots of a darker grey lichen which agrees with Weddell's Z. prosechoides 

 var. aeruginosus. Although P. lobulatum and L. prosechoides are frequently 

 found growing together, L. prosechoides is more common on the shady steep 

 eastern faces of the cliffs; while P. lobiilatumlikeB sunshine and is more usual 

 on the south and south-westerly slopes, on very sunny exposed rocks being 

 always of a much browner colour than usual. 



Physcia parietina, \\\iB most foliaeeous licliens, requires a fair supply of 

 moisture and some protection from severe winds. On sunny sheltered rooks 

 it is of a brilliant colour and is always well fertile. On more exposed rocks 

 and in shade it seldom produces apothecia. In deep shade the tliallus is 

 always of a greenisli colour. 



Some of the most extensive colonies of Physcia parietina found on the 

 Howth coasts occur on the top of the cliffs at Drumleck Point. The cliffs 

 here rise almost perpendicularly, and at about 60-80 feet above sea-level 

 slope back at a low angle like the roof of a house. These rocky slopes pass 

 upwards into a gravelly bank studded with Statice, Crithmum, and Plantains. 

 The rock-surface near the edge of the cliff is covered with a mixed growth of 

 Placodium lobulatum and Lecanora prosechoides, with here and there a few 

 plants of Spergularia rupestris and Cochlearia officinalis in the cracks and 

 fissures. Further from the edge where the surface is rougher and on the 

 stones embedded in the bank above, Physcia parietina is a sheet of colour. 



SOIENT. PROC. K.D.S., VOL. XIV., NO. VI. Q 



