ALPINE PLANTS. 3 
ation is less felt, as summer rains _ bring 
down warmth from above to add to their 
natural heat. The sun heats the surface of 
the soil, no doubt; yet, even in the hottest 
weather, its heat descends only a few inches, 
but when rain falls upon the warm surface 
and finds an easy descent (as it does on 
well-drained soils), the earth itself becomes 
warmer, and the heat is carried down to the 
under-soil. The roots of the plants receive 
the benefit, and general growth is stimulated 
thereby. 
As a brief illustration: In the case of un- 
drained land, where the rain falls upon a 
surface which becomes baked and hard, it 
immediately runs over the surface, dissolving 
any soluble matter lying on it, and carries 
it into the nearest hole or on to the walks. 
In this manner rain thus injures rather than 
benefits the land. 
But it is quite another matter if the rain 
can penetrate where it falls; then, whatever 
it dissolves it carries down to the roots of 
the plants and distributes any saline matters 
which have a tendency to rise to the 
surface, thus promoting growth by bringing 
B 2 
