PRACTICAL ARBORICULTURE 81 
ductions of farms have so decreased that business for boats no longer exists as in 
former times. 
It is not fully recognized that the forests very largely control the transpor- 
tation of produce, both on land and upon inland waters, but this is nevertheless 
true. 
As we have shown, erosion from hills and farms, filling the streams with 
silt, has been the principal cause of irregularity of depth in the waters of rivers, 
and a hindrance to free navigation. One of the great items of expense in the 
A KOREAN PORTER 
United States is the river and harbor expenditures, to overcome this filling up of 
the channels, which each year is giving greater trouble. 
Then electricity is controlled by forest trees which are the principal means of 
communication between the earth and the clouds, and as the volume of water 
which the atmosphere can retain is altogether regulated by the presence of a greater 
or less quantity of the electric fluid, the presence or absence of ample forest bodies 
