2 Alpine Plants. 
moisture which is essential to the maintenance of 
plant life. 
The admission of frequently renewed supplies of 
air into the soil is of equal importance to its 
fertility, and the possibility of this also depends upon 
drainage. 
When rain falls upon the surface of well-drained 
land, it makes its way into the innumerable extremely 
minute channels which run among the particles of 
soil, expelling before it the air with which they were 
previously filled ; then, on the diminution or ceasing 
of the supply, the surplus water runs away rapidly 
through the fissures of the mould, and as it leaves 
the pores of the soil empty above it, is followed by 
the air, which fills in renewed volume the numerous 
cavities from which the descent of the water had 
driven it. When land is ill-drained, it remains full 
of water, and no such renewal of air can take place. 
The condition of the drainage modifies, in an 
equally striking manner, effects due to the tempera- 
ture of the falling rain. 
If the temperature of the rain as it falls through 
the atmosphere is higher than that of the surface 
soil upon which it falls, the latter is heated by it. 
Should, therefore, the rain be copious and sink easily 
into the subsoil, it will carry warmth with it through- 
out the whole body of earth. 
Hence drainage plays an invaluable part in respect 
to local heat-supply ; the undersoil, in well-drained 
places, being warmed, and the effects of evaporation 
reduced, as the rains of summer bring down warmth 
from above to add to the specific heat of the soil, 
