The Ecology of the Driva Valley. 367 
Philonotis tomentella, a form of Dicranum Bonjeanii, Amblystegium 
fiuitans, A. e-xannulatum , A. cordifolium, A. aduncum, and A. 
intermedium. In the tiny streams slowly finding their way 
into bogs were dense cushions of the gregarious Koenigia islandica, 
occasionally associated with Montia fontana and Epilobium alpinum. 
VIII.— Alpine Lichen-Pasture. 
[Marked L on the Chart.] 
Above the somewhat indefinite limit of the shrubs one passes 
into the alpine pasture, which in a great measure consists of 
fruticose lichens: so much so, in fact, that the whole of this 
upland area is really an extensive lichen-formation. This great 
expanse of lichens exist not merely where the ground is rocky and 
precipitous, but also covers square miles of the more or less level 
upland areas. Walking over this lichen-formation gives rise to 
peculiar sensations, as the lichens are from three to five inches in 
depth. In wet weather it is a carpet of softness beyond conception; 
in the hot sunshine every step crushes a number of these upstanding 
lichens into fine powder. This lichen-formation constitutes the 
pastures of the reindeer, and consists chiefly of the following six 
lichens :— Platysma nivale (with P. cucullatum in small patches), 
Cladonia sylvatica var. alpestris, Cl. rangiferina, Alectoria ochroleuca 
(and small quantities of A. rigida), Stereocaulon alpinum , and 
Cetraria islandica. The first-mentioned was generally dominant, 
and the others locally so. The Alectoria , when dominant, was in 
the most exposed places. Other lichens occurred sparingly amongst 
those already mentioned, the chief of which were:— Cetraria acu- 
leata, Cladonia degenerans, Cl. fareata, Cl. cariosa, Cl. gracilis (and 
its var. macrocera), Cl. cervicornis, and Sphcerophorou coralloides. ' 
Flowering plants are dotted amongst the lichens, either as 
individuals or in clusters, sometimes in widely open formation and 
at other times in much closer formation. Lychnis alpina often 
stands out conspicuously ( vide PI. 2, Fig. 2), and great cushions of 
Silene acaidis are common up to 4,750 feet. These large mat-like 
cushions of Silene acaulis are quite a feature of the open phanero¬ 
gamic formation, and often reach a diameter of two feet. An 
examination of the leaf-structure, shows the stomata to be exclusively 
confined to the upper surface, a fact which is correlated with the dense 
character of the mats, only the upper surfaces of the leaves being 
freely exposed to the air. 
