10 BULLETIN 255, U. S. DEPARTMENT OF AGRICULTURE. 
original wounds made by individual specimens may be several feet 
epart on the trunk of a tree, as the latter grows taller and is swayed 
by the wind the inflexible blisters are gradually lengthened and 
widened and finally united. In trees which had been infested on all 
sides the seams are entirely circular, while in those infested on one 
Fie. 4.—Work of the Douglas fir pitch moth: Pitch blister two years 
aiter emergence of moth, with tissues which had already grown over 
it perfectly, removed at one side. Natural size. (Original.) 
side only, a frequent occurrence, the seam is semicircular. However, 
the cause which underlies both these effects is the same. 
EVIDENCE THAT IT IS INSECT WORK: 
(Figs. 6-8.) 
Full-blown pitch seams probably never pass into lumber, and 
affected parts of logs are either converted into small “ dimensions,” 
