206 FIRST BOOK OF FORESTRY 



If now we sprinkle again, but very hard this time, we 

 see that the water washes out gullies arid carries away 

 the soil, just as we all have seen soil carried from plow-^ 

 land, and just as many thousands of acres of plowland 

 in Mississippi and other states have been gullied and 

 ruined by water. Let us now cover part of the layer of 

 earth on our table by a one-inch cover of moist cotton 

 batting. Repeating the sprinkling, we find that this 

 cover of cotton does two distinct things : it protects the 

 soil and keeps the water from carrying it away ; in addi- 

 tion, it keeps the soil moist for hours after we cease 

 sprinkling. This is exactly what the forest does : the 

 torrential rain finds a canopy of twigs and leaves to 

 break its force, and when the water reaches the ground 

 it finds a layer of leaves which prevents it from carrying 

 away the soil. In addition, a network of numberless 

 roots holds this earth for a considerable depth, and the 

 many dead roots of former trees have softened the soil 

 and made it more penetrable ; thus, the water soaks in 

 instead of running off. 



That grass and other herbaceous vegetation cannot 

 well replace the forest in this respect is clearly shown 

 by the fact that the Missouri River and its tributaries, 

 which come from prairies, are muddy torrents after every 

 rain, while the streams of the dense forests run clear and 

 are undisturbed by ordinary rains even though they have 

 a greater fall. 



