DOUGLAS FIR PITCH MOTH. 



9 



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 is impossible and a serious defect is evident almost immediately, 



Pig. ::.-- Work «f the Donglae flr pitch moth: Effect of Infestation on the 



wood growth L> inches below (and above) the wound the first year after 

 attack. ( Original. ) 



even without the added aggravation of mechanical wind strain. 

 The effed 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 leg is inflicted while the 

 than 50 years old, and most of the pitch seams, which 

 n- nit more or Less in a separation of the inner and outer (issues, 

 are. caused by the insect when the trees arc quite young. 'While the 



93335° Bull. 255 -15 2 



