56 
THE GARDEN OF THE WORLD 
in places where the rain falls often and the 
surface of the earth is always moist. 
Where the soil is sandy or coarse, and rain 
falls only occasionally, the roots must go deeper 
into the ground because the water does not stay 
on the surface but soaks in. Sometimes it goes 
down several feet until a bed of clay or rock 
holds it. There it lies until it has been used up 
for there is no air to make it evaporate. Plants 
which grow in very dry places often have root 
systems many times larger than the plants them¬ 
selves. They branch out sideways in every di¬ 
rection and go deep down into the earth as well. 
They must be sure of getting every drop of the 
precious water when there is any. The prickly 
pear cactus, for example, often has roots that 
extend at least five feet on each side. 
Trees, of course, must have very big roots to 
make a firm support for the heavy weight of the 
tree. A tree needs an enormous amount of 
water; so the roots branch out in all directions 
and especially go deep down into the earth to 
get all of the moisture possible. The big 
