GRASSLAND AND WOODLAND 25 
land left undisturbed because unsuitable for cultiva- 
tion—on heaths and moors, in swamps and lakes, on 
sea-sands, chalk downs, and so on; and even in most 
of these places intensive grazing of domesticated 
animals and other causes connected with human 
activities alter and control plant life to a greater or 
less extent, rendering it necessary for us to walk 
warily in our study of it. 
Although the world offers many different aspects 
of closed vegetation, they may all in a broad sense be 
reduced to two general types—namely, grasslands 
and woodlands, the former the result of a lighter, the 
latter of a heavier, rainfall: grasses and their associ- 
ates requiring for their life-processes a much less 
amount of water than a tree vegetation. The British 
Isles lie within a broad belt that sweeps east and west 
across Europe, characterized by a prevalence of 
south-west winds laden with moisture, and yielding 
a tolerably heavy rainfall distributed throughout the 
year. South of this belt—south of the Alps, roughly 
—the rainfall occurs chiefly in winter, and dry 
summers produce the well-known “Mediterranean 
climate” with which is associated the scrubby small- 
leaved vegetation, capable of withstanding heat and 
drought, which is characteristic of Spain, Italy, 
Greece, and Northern Africa. Northward, the forest- 
belt extends into Scandinavia, dwindling into a 
tundra vegetation of lowly shrubs and herbs as we 
approach high latitudes with a sub-arctic climate. 
Forest, then, is the original and natural type of vegeta- 
tion of the British Islands, and without doubt the 
greater part of the country was occupied by wood- 
land within the human period. But forest country 
