LICHENS OF ARRAN 249 



lichens constitute the principal components of a well-marked 

 lichen-association on the barer sandstone rocks just above high- 

 water mark. Most of the foregoing species were also noted on 

 quartz-porphyry, an acid igneous rock which is very promi- 

 nent at Drumadoon Point and other localities on the Arran 

 coast. A few species were found to occur not only on sandstone 

 and acid igneous rocks, but also on igneous rocks of basic type, 

 e.g., basalt, but unfortunately the lichen-flora of the basic rocks 

 was not sufficiently examined to yield data for comparative 

 purposes. It may be mentioned that certain lichens (e. g., Verru- 

 caria nigrescens, V.maculiformis, Placodium tegularis, and P. lobu- 

 lation), which in many parts of the country are restricted to 

 calcareous rocks, were observed on siliceous rocks on the Arran 

 coast. From this it would appear that these exposed, spray- 

 washed maritime rocks afford the requisite xerophytic conditions 

 which in other districts are only furnished by limestone, and the 

 chemical composition of the substratum does not come into 

 question in these cases. As bearing on the question of the part 

 played by the texture or grain of a rock- surface so far as some 

 lichens are concerned, it may be mentioned that on the Arran 

 coast the sandstone, when adjacent to intrusive igneous rocks, is 

 usually close-grained and indurated, and that several species, e. g., 

 Lecanora squamulosa, L. picea, Lecidea rivulosa, and Bhizocarpon 

 petrceum, were found on this type of rock, and were not seen on the 

 unaltered sandstone. The coarse conglomerates, such as are met 

 with near Corrie, are poorer for lichens than the sandstones, this 

 being probably due to the fact that when the sandstone matrix 

 weathers, a very uneven surface, mainly consisting of quartzose 

 pebbles, results. The granitic rocks were not much examined, 

 but at the lower elevations, at all events, the granite is charac- 

 terized by a paucity of species ; on the exposed crags of the high 

 peaks, however, some of the boreal lichens found on other Scotch 

 granite mountains may be expected to occur. 



In the following list, one hundred and nineteen species of 

 lichens are enumerated. It must be understood, however, that 

 our list does not at all pretend to represent the lichen-flora of the 

 island : it is simply a catalogue of the lichens collected and 

 observed during a holiday visit, supplemented by a few previously 

 published records which have come under our notice. 



Lichina confinis Ag. On sandstone rocks at tide-level, Corrie- 

 gills. A form also occurs in the same locality, on boulders well 

 above high-water mark, in which the spores are monostichous, but 

 slightly different in shape and measurement from the normal 

 (16-5-19-5 X 13-2 p). 



Collema furvum (Ach.) var. tunceforme Nyl. On sandstone, 

 Corriegills shore. — C. pulposum (Ach.) c.frt. Among mosses, on 

 earth, Corrie, West. 



Synechoblastus nigrescens (Ach.). On an ash, Monamore Glen, 

 West. A more divided form than usual, and, perhaps, may be 

 a distinct variety. 

 Journal of Botany. — Vol. 51. [August, 1913.] u 



