THE NAVAL STORES INDUSTRY. 11 
The additional ducts require from 2 to 4 weeks for their formation 
full of resin. 
If a new cut is made just above the old one, after the additional 
ducts have had a chance to form, the flow will show a large increase 
over that obtained from the original wound, due to the additional 
ducts. 
Depth of cut — Since the additional ducts form only in the cam- 
bium layer, and since they yield by far the greater part of the resin, 
cutting deeper than this layer induces but little additional flow. In 
commercial operations the depth of the cuts or " streaks" runs from 
one-half to one inch. Such streaks are, of course, much deeper than 
necessary, and to just that extent tend to reduce the vitality of the 
tree and, in consequence, its ability to give a sustained flow. Tests 
have shown that a greater average flow over a four-year period can be 
obtained from trees with streaks 0.4 inch deep than from trees with 
streaks 0.7 inch deep. In any case, shallow streaks give fully as large 
a flow of resin as deep ones, when the period of tapping extends over 
two years or more. The tools used at present, however, make it 
difficult to cut shallow streaks, while the custom of deep chipping is 
pretty firmly established through long usage. 
HeigM of chip. — When a new " streak" is made the flow of gum is 
at first comparatively rapid, but gradually decreases until at the end 
of a week it has practically ceased. The diminution of flow is pre- 
sumably caused by the gradual hardening of the resin in the exposed 
ends of the ducts, which results in plugging them. It then becomes 
necessary to chip again. In deciding how thick a chip should be 
taken off, or how much the "face" or scar should be increased in 
height to give a new flow, it should be remembered that the bulk of 
the resin is produced in the region between the wound and a point 
about two inches above it. For this reason, no more of the wood 
immediately above the old wound should be removed than is necessary 
to open up the ends of the resin ducts in which the gum has hardened. 
Since in the space of a week the resin does not harden in the ducts for 
a distance greater than one-fourth inch from the surface of the cut, 
a chip that increases the height of the face one-fourth inch is all that 
is necessary. In practice, the vertical height of the new streak fre- 
quently exceeds 1 inch, thus eliminating practically one-half of the 
wood where most of the resin is being produced, and decreasing the 
productive period of the tree four times as rapidly as necessary. 
With the present type of tool it is difficult to cut a one-fourth inch 
streak, and, moreover, the difficulty of changing an old established 
custom again presents itself. The chipping tool should always be 
sharp. A dull edge tends to crush the ends of the resin ducts instead 
of cutting them clean, thus preventing a free flow. 
