Page:Popular Science Monthly Volume 91.djvu/362

 ���Like a dentist he removes all de- cayed matter from a cavity

��THE science of tree surgery is but twenty years old. Yet it has already become of inestimable value. It is saving thousands of shade trees and fruit trees each year. All trees, and sweet- sapped trees especially, are liable to fungus disease. The fungus is a parasite by nature and sends little, thread-like tentacles into the woody tissue. These travel from cell to cell, disintegrating the internal structure of the tree. The result is what we call "rot." When fungus starts in a tree it never stops unless ar- rested by human skill. The tree surgeon alone can destroy the disease.

The accom- panying illustra- tions show how useful tree sur- gery can be. In one of the illus- trations is shown steel cables strung between

the upper a sick tree on the way to

branches so that filling reaches almost to

��Operating Upon Trees

When trees get sick or are dam- aged they need the tree surgeon

��the weakened trunk would not be unduly strained under the action of the wind. This was a comparatively easy task, but real tree surgery is not simple. It is a diffi- cult and exacting art. Some trees require a combination of bolts and lock-nuts, rein- forcing rods and cross-bolts with lock-nutr; above the crotch. Others need a combina- tion of bolts and criss-cross bolts with lock nuts, tortion rods and chains, and still others call for iron straps, tortion rods, iron backbone and ribs in addition to chains and la*g-hooks higher up.

Another illustration shows large cement fillings built up in separate block sections to allow swaying of the tree. In a very short time, the edges of the cut "heal" to the cement. That is, the soft living tissue solidifies upon the cement, making a tight joint which is waterproof. Often the bark at the sides of the patch gradually grows to- gether closing

���health. The cement the heart of the tree

��over the cement. Young trees are not so difficult to doctor. One of their chief ene- mies is the bore worm. The tree surgeon, upon discovering a worm hole in the tree drills into it with a stiff wire, kills the worm and fills up the hole with tar.

But tree sur- gery is not merely a matter of filling cavities. Unless the work is scien- tifically accurate and mechanical- ly perfect, it fails. Since decay de- stroys the struc- tural strength of the tree, this strength must be restored by me- chanical means.

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