10 BULLETIN" 255, IT. S. DEPARTMENT OF AGRICULTURE. 



original wounds made by individual specimens may be several feet 

 apart on the trunk of a tree, as the latter grovrs 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 





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Fig. 4. — Work of the Douglas fir pitch moth : Pitch blister two years 

 after 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-S.) 



Full-blown pitch seams probably never pass into lumber, and 

 affected parts of logs are either converted into small " dimensions," 



