Callusing and Repairing Ol 
applied, while in spring the oozing sap of many species will 
prevent the paint from sticking or the tar from penetrating. 
If pruned in the fall, the wound wood begins to form in 
the early spring and is well advanced before the fungus 
spores begin to fly. The com- 
parative absence of fungus 
spores in late fall and the fact 
that the form of the tree is 
better visible when the foliage Fic 21 — Malleable pruning 
has left it also favors this season shears 
as compared with the summer. Only those species, 
which, like the maples and birches, are apt to bleed freely 
even late in the autumn and early in spring, are best pruned 
in winter or late summer, although the bleeding is in the 
main detrimental only because it prevents the paint from 
adhering. 
Callusing and Repairing. We will now briefly look at 
the healing process, a knowledge of which will be useful 
to the pruner and will assist his judgment, especially as to 
where and how to locate most advantageously the cut 
in trimming, pruning, and repairing. 
When, in the natural order of things, a leaf falls, or a 
piece of bark is sloughed off, as is so conspicuously done 
in the sycamore, this loss of parts 
has been gradually prepared for 
and the wound is already cov- 
ered securely by a cork layer, or 
Fig 22. eer shearing 4 temporary covering has at 
least been provided for by the 
formation of gum or resin, before this final voluntary loss 
occurs. When an involuntary physical injury, as the tearing 
off of a piece of live bark or the breaking of a branch, takes 
place, a similar process of providing a covering of the wound 
