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) surface wounds, which do not extend beyond the inner bark, and (2) deep wounds or cavities, which may range from a small hole in a crotch to the hollow of an entire trunk.
Surface wounds: Surface wounds ([Fig. 116]) are due to bruised bark, and a tree thus injured can no longer produce the proper amount of foliage or remain healthy very long. The reason for this becomes very apparent when one looks into the nature of the living or active tissue of a tree and notes how this tissue becomes affected by such injuries.
Fig. 116.—A Surface Wound Properly Freed from Decayed Wood and Covered with Coal Tar.