44 FIRST FORMS OF VEGETATION. 
and spread over wider areas in ‘islands and the 
vicinity of rivers and lakes than in the interior of 
continents, unless when well wooded and watered. 
Their favourite habitats appear to be rocky dells or 
ravines at the foot of mountains, with streamlets 
murmuring through them, and dense trees inter- 
weaving their foliage over their sides, and creating 
a dim twilight in the recesses beneath. In such 
hermit seclusions the botanist may expect to reap 
the richest harvest of species. 
Mosses occasionally select very singular places 
of growth; and notwithstanding the minuteness 
and profusion of their seeds, the facility with 
which they can be disseminated, and their insensi- 
bility to ordinary physical conditions, are, specifi- 
cally considered, sometimes very much restricted 
in their geographical range. Several kinds are 
found in this country only on the summits of the 
highest Highland mountains, covering the barren 
soil with a thin film of verdure, or creeping over 
the weather-beaten rocks in tenacious dark-col- 
oured clusters or tufts. These species are iden- 
tical with those found on the plains of the Arctic 
regions and the hills of Lapland and Greenland, 
where they occur not merely in isolated tufts, as 
we find them in this country, but carpeting the 
ground for many yards, and imparting a verdant 
hue to the mountains and valleys. This circum- 
