chap, vii.] WALL-FRUIT TREES. 197 
instead of suffering them to spread through 
the arches to the other sides, where they are 
entirely removed from him. 
The essential point to be attended to in the 
construction of a fruit border is that the soil 
shall not be more than eighteen inches deep 
on a hard bottom. If the subsoil be hard 
gravel or rock, covered with mould to the 
depth mentioned, nothing more can be de¬ 
sired ; but if the subsoil be wet clay, or sand 
over gravel, or in short anything that will 
allow of roots penetrating into it, artificial 
means should be resorted to, to keep the 
roots near the surface of the ground. The 
most common method of forming a border is 
to excavate the ground to the depth required, 
and to pave the bottom of the excavation 
with large stones or pebbles ; but bricks, 
cement, asphalt, or in short any other sub¬ 
stance may be employed which appears likely 
to attain the end in view—taking care, how¬ 
ever, to provide effectual drainage, as other¬ 
wise the chamber, as it is called, would be¬ 
come a reservoir of stagnant water, exceed¬ 
ingly injurious to the plants. The chamber 
having been formed, it should be covered 
