84 BRITISH PLANTS 
The Relations between Soil and Climate. 
In Chapter I. we considered the factors determining 
climate, and we learned that differences in the vegetation 
are associated with differences in climate. But climatic 
conditions are the same over wide areas, and yet marked 
and profound differences may be found in the flora. We 
cannot go far from our doors without seeing this. In 
some localities we may, in a few hours’ walk, pass by cul- 
tivated fields, wet meadows, rough fields, dry pastures, 
reedy swamps, and several kinds of woods and thickets. 
The climate is the same for all ; it could hardly vary in 
the course of a short walk. The same is true when we 
examine the vegetation in an upward direction. Hills 
of the same height may carry very different kinds of 
plants. One may be covered with reedy bogs, another 
with gorse and heather, and another with grassy pastures. 
Wood differs from wood, and field from field. Even in 
the same field, when we come to details, many differences 
are apparent ; the vegetation on the dry rising knolls is 
not the same as in the damper hollows, and disturbed 
patches can be detected by their distinctive plants, even 
from a distance. What is the cause of all this variation 
within the limits of practically the same climatic condi- 
tions ? It is the soil. All soils do not react in the same 
way to climate. The sun’s rays will warm one kind of 
soil much more than another ; with the same rainfall some 
soils become wetter and remain wetter than others. In 
a short journey we may tread many kinds of soil, each 
bearing its own characteristic plants. Climate deter- 
mines the broad features of the vegetation, but the minor 
differences in the flora are due to the character of the soil 
and the way it behaves towards the external sources of 
heat and moisture. 
The relations between soil and climate must therefore 
be considered under two aspects : 
I. The reaction of the soil to water. 
Il. The reaction »f the soil to heat. 
I. Soil and Water.—The ~\ost important soil or edaphic 
factor is the amount of a ailable water present. This 
clearly depends upon— 
