PLANTS AND HABITATS 23 
adaptation to given surroundings, limiting conditions 
of life: where these conditions are exceeded, the 
desert supervenes. Thus, the salt-marsh is a desert 
to almost every plant of the mild open soil of hill or 
valley, just as the hills and valleys are deserts to most 
of the inhabitants of the salt-marsh. The alkaline 
soil of the rock crevices of Farleton Fell is fatal to 
some of the most abundant plants of the acid peaty 
soil of the hills, such as Ling (Calluna vulgaris) 
and Bilberry (Vaccinium Myrtillus). For another 
cause—the diminution of light—the deep woods are a 
desert for many plants of the sunny pastures, and 
vice versa. Plants vary very much as to their degree 
of adaptability to different soils and different climatic 
conditions. Some are highly specialized. Our salt- 
marsh flora, for instance, is, as regards most of its 
species, confined to its peculiar habitat. If on a map 
of Europe we coloured in its distribution we should 
find it formed a ribbon round the coast, except for a 
few dots where the plants have discovered inland 
salt springs or salt lakes, and have found their way 
to them. Most plants are more adaptable than these, 
and occupy a variety of habitats. The little Tormentil 
(Potentilla silvestris), for instance, flourishes equally 
on hot banks by the sea, in woods, and on mountain- 
tops. The more accommodating a plant is as regards 
habitat, the wider its distribution tends to be, both 
locally and in a broader sense. But wide range does 
not follow of necessity from adaptability to a variety 
of conditions: the problem of plant distribution is not 
so simple as that. One species may be spread right 
round the world, yet be always found in a special 
habitat; take the case, for instance, of the Yellow 
