DOUGLAS FIR PITCH MOTH. 79 
becoming rather deeply embedded in the woody tissue. From then 
on it depends upon the growth of the tree whether only the pitch 
blister at the base of the wound is to be inclosed in the healthy tissues 
or whether the pitch from the pitch tube and bark also is to be in- 
closed. As a rule, a tree of slow growth heals from the inside and 
the injury is less apparent, whereas a tree of rapid growth puts forth 
such a quantity of new growth over the injured spot that clean heal- 
ing 1s impossible and a serious defect is evident almost immediately, 
Fie. 3.—Work of the Douglas fir pitch moth: Effect of infestation on the 
wood growth 2 inches below (and above) the wound the first year after 
attack, (Original.) 
even without the added aggravation of mechanical wind strain. 
The effect of mechanical strain during succeeding seasons upon trees 
afflicted with serious wounds from the very beginning renders them 
unfit as lumber material. : 
The real depreciation of the future saw log is inflicted while the 
trees are less than 50 years old, and most of the pitch seams, which 
result more or less in a separation of the inner and outer tissues, 
are caused by the insect when the trees are quite young. While the 
93335°—Bull. 255—15 2 
