14 



BULLETIN 255, U. S. DEPARTMENT OF AGRICULTURE. 



This has to be borne by future generations, just as the present is 

 paying for the damage inflicted by the insect a century or more in the 

 past. 



Actual tally of sesiid wounds, blazes, bullet wounds, bruises by 

 blasting, etc., all of which cause blister effects in wood tissue, was 



Fig. 8. — An embryo pitch seam caused by the Douglas fir pitch moth 

 only a few years after emergence of moth : A, Pitch blister which 

 the larvae caused before emerging ; H, a break in the tissues by 

 wind strain on account of the defect ; C, break filling with pitch ; 

 D, inclosed pitch from pitch tube which caused imperfect heal- 

 ing; E, parts of pitch tube which covered the larvse, still part of 

 the surface covering. Reduced. (Original.) 



made in a stand of Douglas fir about 30 years old, where conditions 

 were most favorable for the operation of all the latter causes. This 

 tally demonstrated that in this area of about 30 acres the sesiid 

 wounds averaged, up to 15 feet from the ground, a little over 96 per 

 cent, while the wounds from all other causes combined represented 

 less than 4 per cent. Wounds above 15 feet could safely be consid- 



