REPAIR OF SHADE TREES 
161 
done in spring, by the use of dormant shoots or twigs of 
the previous year’s growth somewhat longer than the bare 
place, affixed perpendicularly under the freshly trimmed 
edges of the bark to bridge the wound. The ends of the 
twigs are trimmed wedge shape, and these sharp ends are 
inserted between bark and wood, beneath slits in the bark 
above and below the wound. When properly placed, they 
form a bridge through which the sap may flow. To hold 
the bridge in place, a cloth bandage should be tied around 
each edge of the bark. To prevent drying, the ends of the 
bridging twigs should be coated with melted grafting wax. 
This wax may be made of four parts of resin, two parts of 
beeswax and one part of tallow, melted together and 
worked with greased hands, in cold water, until it becomes 
grainy. Success with bridge grafting depends upon close 
contact of fresh cambium layers of scion and stock at both 
ends, with immediate protection from further evapora¬ 
tion by thorough and careful waxing. 
Cavities offer serious problems in the life of a tree and 
require careful treatment. Minor cavities may be cared 
for by the layman, without previous experience, if simple 
rules are closely followed, but in the case of a large one it is 
unwise for the work to be undertaken by any but the 
technically trained expert. 
One of the commonest causes of decayed cavities is 
the protruding stub left from careless pruning. Unless 
the limb has been cut without leaving a stub, rot will start 
which, sooner or later, will spread its decay into the trunk. 
Similar results come from neglected surface wounds. In 
the course of time troubles thus started imperil the life 
of the tree. 
In the treatment of cavities it is most important that 
no trace of dead or diseased wood be allowed to remain. 
The basic principle is to make sure that all decay is 
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