INJURIES TO SHADE TREES 



153 



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. 



