PRESENT CONDITION OF BRITISH ISLES 31 
or natural grass, over which wander great herds of 
sheep and cattle. A. G. Tansley* thus contrasts (in 
percentages) the area of cultivated land (on which 
natural vegetation has been to all intents destroyed), 
with the area on which natural or semi-natural con- 
ditions still prevail: 
England. Wales. Scotland. Ireland. 
Cultivated land na ale 75 59 25 ? 20-30 
Land under natural or semi- 
natural vegetation she 15-20 40 70-75 ?70-80 
It will be seen how little of the original vegetation 
of England is left to us for purposes of study—less than 
one-fifth, almost the whole of which has been influenced 
to some degree by human operations; while in Scotland 
and Ireland a much larger area is more or less in its 
primitive condition. The Scottish mountain-sides and 
Irish moorlands still to a great extent retain a natural 
flora, save that the greater number of grazing animals 
which they now support, as compared with the times 
when wolves and other enemies roamed unchecked, 
leaves its impress upon the vegetation. 
Viewing the plant world as a whole, its primary 
divisions, from the point of view of ecology, are 
governed by the factor of rainfall. It is true that 
the plants of the Tropics differ profoundly from those 
of the Temperate regions, and those again from the 
plants of the Arctic. But this is a difference in the 
species and families which constitute the vegetation, 
rather than a difference in the types of vegetation 
or plant formations which occur. A certain area in 
Siberia may not have one species in common with a 
certain area in India, but in both we may find the 
‘* Types of British Vegetation,” 1911, p. 63. 
