Knowles — The Maritime and Marine Lichens of Howth. 121 



3. CorticoloKS Lichens. 



There are no trees in our area, and consequently corticolous species are 

 very scai-ce. The Blackthorn scrub on the cliffs overlooking Broad Strand 

 supplies almost the only habitat for these lichens. The main part of the 

 collecting was done below Earlscliffe. The scrub here is composed almost 

 entirely of Blackthorns ; a Whitethorn occurs here and there, but no 

 different species were noticed on these. Gorse and Bramble stems and an 

 Elder bush were also searched, but they yielded no lichens. One species, 

 Bilimbia Naegeli, was collected on lieather-stems on the south-west coast ; but 

 with this exception all tlie others are from the Blackthorns. As the scrub is 

 extremely dense and the light very subdued in the interior, most of tlie 

 lichens grew on the outer fi-inge of the thickets or on the twigs and branches 

 on the top surface. The lichen-growths were nowhere abundant or vigorous, 

 but they showed a tendency to occur in strata, the Ramalinas and Evernia 

 being more usual on tlie scrub of the upper part of the bank where there was 

 more breeze, while the Physcias and crustaoeous species were more common 

 on the thickets in the lower reaches. Evernia jJi'unastri and three species 

 of Eamalina — B. fastigiata, B. farinacea, and B. intermedia — were about 

 equally abundant, but none of them was really plentiful; tliey mostly occurred 

 as tufts on the smaller twigs and branches in the upper thickets. Several 

 Parmelias — P. sulcata, P, exasperata, P. laevigata — covered the upper 

 surfaces of the larger branches. The Parmelias seem to require a certain 

 amount of shade and protection from wind ; but they were not found in the 

 interior of the thicket where the light was dim. Physcia lychnea was very 

 general on the Blackthorns nearer the shore, and seemed to flourish best in 

 the forks of the small branches, its patches of greenish-yellow fronds being 

 usually fertile. In deep shade it was much greener in colour, but took ou a 

 yellowish hue, and seemed to be more generally fertile where the light was 

 stronger. Physcia aipolia, and P. tribacia were occasionally found in the upper 

 stretches of scrub and with tliem P. pulverulenta, P. tenella, and P. pityrea, 

 the last-mentioned species being barren and much rarer than any of the 

 others. Several crustaceous lichens were also collected ; Buellia myriocarpa 

 was comparatively plentiful both on living and on dead wood, Lecanora varia, 

 L, angulosa, L. chlarona, Binodina sophodes, Lecidea parasema, L. elaeochroma 

 were general, often growing mixed up together on the same branch. Artho- 

 pyrenia epidermidis, Acrocordia gemmata, Graphina inusia, Pyrenula nitida, and 

 Lecanora symmictera also occurred, but were scarce. 



On the smooth shining bark of the Blackthorns lichens are not really 



b2 



