CHAPTER XVIII. 
THE PHILOSOPHY OP DEEP DRAINAGE AND CULTIVATION IN THEIR 
RELATION TO THE GROWTH OF TREES, AND THE SUCCESSFUL CUL¬ 
TURE OF THOSE WHICH ARE HALF-HARDY; TOGETHER WITH SUGGES¬ 
TIONS FOR PROTECTING YOUNG TREES IN WINTER AND SUMMER. 
A LARGE portion of the gross weight of all soils is water. 
If we dry any soil perfectly, the residuum of weight will 
bear a very small proportion to the average weight of 
the soil in its natural condition. Water, therefore, occu¬ 
pies a large part of the texture of what we call solid earth. When 
we draw the water from any soil by drains, the space occupied by 
the water in the earth is supplied by air. Thorough draining, 
therefore, airs the soil to whatever depth it drains off the water. 
The air transmits heat and cold less rapidly than water by direct 
conduction, so that, if air occupies the place of water in the inter¬ 
stices of the soil, the latter will feel all changes of temperature 
more slowly. Deep drainage, therefore, tends to equalize the tem¬ 
perature of the earth’s surface, and to neutralize the effect of great 
and sudden changes in the air above. It is impossible to drain a 
subsoil too thoroughly from beneath, because the capillary attrac¬ 
tion of the earth is always sufficient to draw up from below all the 
moisture that is essential to most forms of vegetable life; and in 
addition to the moisture thus drawn from below, the earth, when 
the air can circulate freely in it, has the power when dry to absorb 
a vast amount of moisture from the air, as well as to yield it up to 
the air by evaporation when it holds an excess. To all general 
observations like these, the reader’s intelligence will of course 
suggest exceptions ; as of trees and plants which thrive best where 
their roots are immersed in water, and which make water their 
element rather than earth; but the fact holds good as to the great 
