g a tree, judge its general condition. The trunk of a
tree that shows age, disease, or wood-destroying insects generally has
its branches in an equally unhealthy condition.

2. The different kinds of wood naturally differ in their strength and
elasticity. The soft and brash woods need greater precautions than the
strong and pliable ones. The wood of all the poplars, the ailanthus, the
silver maple and the chestnut, catalpa and willow is either too soft or
too brittle to be depended upon without special care. The elm, hickory
and oak have strong, flexible woods and are, therefore, safer than
others. The red oak is weaker than the other oaks. The sycamore and
beech have a tough, cross-grained wood which is fairly strong. The
linden has a soft wood, while the ash and gum, though strong and
flexible, are apt to split.

3. Look out for a limb that shows fungous growths. Every fungus sends
fibers into the main body of the limb which draw out its sap. The
interior of the branch then loses its strength and becomes like a
powder. Outside appearances sometimes do not show the interior
condition, but one should regard a fungus as a danger sign.

4. When a limb is full of holes or knots, it generally indicates that
borers have been working all kinds of galleries through it, making it
unsafe. The silver maple and sycamore maple are especially subject to
borers which, in many cases, work on the under side of the branch so
that the man in the tree looking down cannot see its dangerous
condition.

5. A dead limb with the bark falling off indicates that it died at least
three months before and is, therefore, less safe than one with its bark
tightly adhering to it.

6. Branches are more apt to snap on a frosty day when they are covered
with an icy coating than on a warm summer day.

7. Always use the pole-saw and pole-shears on the tips of long branches,
and use the pole-hook in removing dead branches of the ailanthus and
other brittle trees where it would be too dangerous to reach them
otherwise.

8. Be sure of the strength of a branch before tying an extension ladder
to it.

STUDY IV. TREE REPAIR

Where trees have been properly cared for from their early start, wounds
and cavities and their subsequent elaborate treatment have no place. But
where trees have been neglected or improperly cared for, wounds and
cavities are bound to occur and early treatment becomes a necessity.

There are two kinds of wounds on trees: (1)