ALPINE VEGETATION ON BEN-Y-GLOE, PERTHSHIRE 231 



Ascending another 700 ft., the summit plateau is reached, 

 consisting of tlie same kind of broken gravelly ground, with 

 scattered stones, and patches of very thin soil, formed chiefly of 

 the debris of cryptogamic plants. The flora at this elevation is 

 slightly different. The dominant plants are Carex rigida and 

 Alcliemilla alpina. 



The quartzite blocks, of which the cairn is built, yield addi- 

 tional Gyrophorce, viz. G. crosa, G. torrefacta, and G. cylmdrica, the 

 first and last-named being very scarce. On loose stones we saw 

 a small quantity of a sterile Pyrenopsis, but Parmelia alpicola was 

 fairly well developed on quartz crystals. On half-decayed patches 

 of Cladonia, Bhacomitrium and Dicranum fmcesceus there is an 

 abundance of Lccanora tartarea var. f rigida, with Lecidea arctica 

 Somm. and L. limosa Ach., on peaty soil fiUing the crevices of the 

 stones. These two lichens appear to thrive in the most bleak and 

 exposed situations offered by our mountains. They are accom- 

 panied by a few starved-looking examples of Thamnolia vermicu- 

 laris, a curious Cladonia-like plant, resembling in shape a small 

 white earthworm. So far as we observed, this Hchen is much less 

 fine and abundant here than in the moss-lichen association of the 

 granitic summits of the Cairngorm range. We saw here the 

 hepatic Gymnomitrium obtusuvi, and no doubt other minute 

 species might have been noted had conditions permitted a more 

 careful search ; but the Bryophyta were not obtrusively evident. 

 Two lichens, Lecidea tabidula Nyl., and L. deparcula Nyl., are 

 recorded by Crombie (6) as occurring on small stones on this 

 summit, but we failed to find them, although they doubtless enter 

 into this association, as also does Lecidea nigroglomerata A. L. Sm. 

 on Cairn Gowar. 



Turning now to ecological considerations, this particular 

 ground, from the broken nature of the surface, which is weathered 

 into stones and gravelly detritus, is subject to rapid drainage, and 

 there is practically no available subsoil water for the plants near 

 the surface. The hard crystalline rock is markedly dysgeogenous, 

 and not retentive of moisture. Any soil formed is either washed 

 down into the interstices, or completely removed by the fierce 

 gales to which these plateaux are exposed. But for the frequent 

 showers and cloud-fog, and occasional pockets in w^iich a little 

 humus is detained by the matted stems of cryptogams, the higher 

 plants would scarcely be able to exist. In such situations the 

 amount of rainfall is of minor importance as compared with its 

 frequency, and probably the plants depend more on the prevalent 

 cloud-mist than on rain for their supplies. There are intervals of 

 bright sunshine and strong wind, producing rapid evaporation of 

 moisture. Added to this frequent desiccation there is consider- 

 able fluctuation of temperature, producing together a set of con- 

 ditions which reduce the possibilities of plant life almost to 

 zero. 



The special contrivances by which certain flowering plants are 

 enabled to face these untoward circumstances are well known and 

 need not be repeated. As regards the Bryophyta, they are mostly 



