153 
INJURIES TO SHADE TREES 
with coal tar, creosote or lead paint as directed under 
pruning. (See page 145) Ragged edges of the bark should 
be pared cleanly with a sharp knife, before treatment, as 
smooth edges heal much better than those which are 
uneven. If the wood has been injured, the damaged part 
should be cleaned out with a knife or gouge before the 
treatment is applied. Bark which 
is merely bruised, but not torn or 
broken, requires no treatment. 
In paring the bark around the 
edges of a wound, special care must 
be taken with the lower edge, as it 
is particularly important that this 
part should be smooth in outline 
and should have no tongues pro¬ 
jecting upwards. The bottom of 
the opening should be rounded 
downward, or better, pointed, and 
its center should be its lowest part. 
This is necessary in order that it 
may more easily receive nourish¬ 
ment from the down-flowing sap. The flow of sap is in two 
directions. Moisture taken from the soil by the roots 
carries its contribution of mineral salts upward, mainly 
through the sapwood to the leaves, and returns towards 
the earth, mainly through the inner bark, after having 
been changed in the leaves by the addition of carbon 
products, taken from the air under the influence of sun¬ 
light. On its downward journey, this altered sap con¬ 
veys and distributes materials essential to growth that 
were prepared in the leaves. The sap travels most 
readily in straight lines, and because of this tendency the 
sides and upper edge of a wound fare best in the matter 
Proper healing of wound in a tree. 
