Knowles — The Maritime and Marine Lichens of Howth. 91 



pass almost imperceptibly into each other. The prevailing form is shown 

 in Plate IV, fig. 2, and for the present it may be called Ramalina A. 



Ranialina A. grows above the ordinary spray-zone, and generally forms a 

 sward-like growth on the weather sides of the lower cliffs, the plants growing 

 both larger ani] closer together along the upper edges wliere the rock and 

 earthy covering meet, or in the neiglibourhood of the various tufts of Thrift 

 or other flowering plants that occupy crevices in the cliff-faces. This is 

 well seen in tlie photograph. In these situations there is a more constant 

 supply of moisture either from surface drainage or from drippings from 

 the leaves of the flowering-plants during rainy weather. 



The thallus of Ramalina A. has a glaucous appearance and is much 

 branched, though it sometimes appears to consist of simple fronds from 

 tho branching having taken place low down near the point of attach- 

 ment. Many of the branches are dilated and fistular and have the upper 

 surface covered with tuberculations, from which, as well as from the sides 

 of the branches, numerous small abortive growths frequently spring. The 

 lower surface of the thallus is usually of a paler colour, and a section shows 

 the gonidia congregated in groups close to the upper surface, while very 

 few are to be seen on the lower surface. Patches of young growths in all 

 stages of development are of frequent occurrence on the barer parts of the 

 rock. Plate VII, fig. 1, shows a sward of young growth of Ramalina A. 

 as it grows on the granite boundary-stones near the Martello Tower, Sutton. 



At higher levels tlie sward-like growths of Ramalina A. disappear, and 

 are replaced by isolated tufts which are scattered irregularly on the rock- 

 surface. At the same time the tliallus becomes smaller and more amorphous, 

 and the pustulations and disorganized areas more numerous. Gradually 

 Ratnalina A. passes into a very small amorphous form which may be called 

 Ramalina B., and which seems to be peculiar to the vertical or almost vertical 

 western and south-western faces of the highest cliffs. 



Ramalina B. — Some idea of the way in which this form grows on the 

 steep rocks of the hill lying close to the sea at Eed Rocks may be got from 

 Plate V. This hill, which is composed of an exceedingly hard and close, 

 grained quartzite, rises to about 210 feet above sea-level. It slopes gently 

 from the crest in a south-east and easterly direction, but the west and south- 

 west sides consist almost entirely of perpendicular rock- walls, the smooth 

 surface being broken only liere and there by an occasional ledge or crevice on 

 which a few plants of Erica and Oalluna have established themselves. 



On these steep rock-walls Ramalina B. is the only lichen growth. On the 

 western faces, indeed, it is the only visible vegetation. The individual tufts 

 are very small and amorplious, with the fronds much lacerated, and are 



