37i 
The Ecology of the Driva Valley. 
Tetraplodon bryoides on old remains of dead animals, and in some of 
wet places Sphagnum rubellum and S. fuscum formed small dense 
cushions, the older masses of which were sometimes covered with 
Bccomyces icmadophilus. On the rocks were Parmelia Janata, 
Gyropliora polyrliiza, G. arctica, G. hyperborea and G. crosa. One 
of these bogs contained quantities of Carex rariflora. Scattered 
through the lichen-formation of this side of the valley were 
numerous cushions of Andromeda hypnoides and Cardamine bellidi- 
folia. Near the rills Saxifraga rivularis was frequent. A form of 
Hypnum palustre was frequent and in the wet glacial mud were 
dense patches of Poldia ludwigii, with Hypnum HeuJJeri, Dcsmatodon 
latifolius and a form of Rhacomitrium canescens on the drier ground, 
the latter among sand. On wet rocks in the streams of melted 
snow, Hypnum Goulardi and H. badium were abundant. 
8a,—The Plateau at the Head of the Valley. 
This agrees in general features with the alpine lichen-pasture, 
but although very bleak the altitude is not so great, and there are 
in consequence quantities of scattered shrubs of Betula nana, 
Juniperns nana, and the dwarf species of Salix (consult PI. 2, 
Fig. 1). 
Stems of Betula nana from this bleak area and also from near 
their upper limit on Knutsho were examined for their structure. 
The amount of wood annually added was by no means small, stems 
eight years of age having a diameter of 5-8 mm. 
Stems of Junipevus nana from the same spots showed growth 
to be much slower. A stem 5-8 mm. in diameter was 30 years old. 
Four concentric series of tracheides was quite a usual number 
to be added in one growing season, and sometimes only two were 
added. The maximum number observed was eleven. 
On the more exposed parts 
the carpet of lichens is very 
thick, and consists of the fol¬ 
lowing species in varying pro¬ 
portions, sometimes one being 
dominant and sometimes 
another :-Stereocaulon alpinum, 
Alectoria ocliroleuca, A. rigida, 
Platysma nivale, P. cucullatuni, Cladonia rangiferina, Cl. sylvatica, 
and Cl. furcata. At the higher elevations Platysma cucullatuni 
became more abundant and P. nivale less abundant. On the 
Fig. 31. Leaves of Betula nana attacked 
by a leaf-blotch fungus {Rhytisma sp.) 
Natural size, 
