24 ON FARLETON FELL 
Bird’s-nest (Vonotropa Hypopitys), a strange colour- 
less, leafless plant, highly specialized, feeding, through 
the intermediary of a minute fungus which infests its 
roots (see p. 183), on the decaying leaves of deciduous 
woods in cold temperate regions, and yet found across 
Europe, Asia, and North America; while many 
other species, at home under very varied conditions 
of soil and moisture, have nevertheless a quite 
restricted geographical range. 
Although our own country, favoured by conditions 
thoroughly suitable to plant life—a sufficiently high 
temperature and an abundance of moisture and light 
—is characterized by a continuous plant mantle—or 
closed vegetation, as the botanists say—nevertheless 
what has been said of desert and semi-desert condi- 
tions applies to many limited areas in the British 
Isles, where the vegetation takes on the peculiar 
characters of true desert plants. Low water-content 
and great exposure produce such conditions on 
shingle beaches and sand dunes; and, as we shall see 
later, the vegetation of sea-rocks, salt-marshes, and 
peat-bogs is in many respects analogous to, desert 
vegetation. 
Except near the Poles, wherever the precipitation of 
moisture rises above an amount which varies accord- 
ing to other conditions prevailing, a closed vegeta- 
tion occupies the ground when the agricultural and 
other operations of man do not hold it in check. But 
as much of this favourable region is utilized by the 
human race for the production of plants used for food 
or for industry, it often happens, as in our own 
country, that the natural plant communities are to 
a great extent destroyed, and can be studied only on 
