HOW SOILS L08E WAT J i: 103 



soaks into the soil, where much of it is held as film 

 moistun . To 086 ■ homely illustration, let DJ >uppose 

 water is poured on the head of a perfectly hald person; 

 it quickly runs off from his head, tailing cm his face 

 and person, leaving the head scarcely wet. If, on the 

 other hand, water is poured on tin head of a person 

 with a heavy suit of hair, hut little runs of! till the 

 hair is thoroughly wet. This, in a way, illustrates how 

 growing plants protect land from washing, and cause 

 rain water to enter the soil. 



101. How Growing Plants Stop Surface Evaporation. 

 Growing plants, besides protecting the soil from wash- 

 ing, prevent excessive surface evaporation, which car- 

 ries off much moisture from exposed soils. Sunshine 

 and winds are constantly at work evaporating great 

 quantities of water from exposed fields, leaving the 

 soil dry and hard. On bare fields the loss of water 

 through surface evaporation is enormous. To illus- 

 trate how this loss takes place, let us suppose we have 

 an ordinary bucket half filled with watc '; if left open 

 to sunshine and wind the water in the bucket quickly 

 eveporttetj it passes through the air which fills the 

 upper half of the bucket and disappears into the outer 

 air as water vapor. If the bucket be covered o\ 

 protect it from the wind and >un. much of the evapora- 

 tion kl itopped. Now, the >oil is much like a bucket half 

 full of watrr. We have first a layer of comparatively 

 • il. that is soil containing only film moisture. This 

 ■sponds to the air in the upper half of the water 



bucket Then we have ■ lever of soil filled with i 

 and the whole rests on a bottom formed by the imper- 



