200 Gardening 
Purdue Unio. Agric. Di A 
Fic. 118. A garden in need of cultivation. The surface crust should be 
broken to admit air more uniformly to the roots and to conserve the soil moisture. 
preserving a sufficient supply of water for plants that we 
should thoroughly understand how a surface layer of 
fine, loose soil keeps the water from escaping into the air. 
How a dust mulch prevents loss of water from soil. 
The water in the soil can travel in any direction by pass- 
ing from particle to particle, just as oil travels up the 
wick of a lamp by passing from thread to thread. It 
moves from the places where it is most abundant to the 
places where there is less of it; hence, when the surface 
layers of the soil dry out, the water in the damper soil 
below creeps up toward the surface. In this way the 
water in a soil is brought to the surface and evaporated 
into the air. 
But if the surface layer of the soil is cultivated, it is 
broken loose from the soil below. Then the water 
finds no direct path from particle to particle upward ; 
the connection of the upper layer with the soil below is 
broken. Hence the surface soil soon dries out because its 
