Figure 2 .- -Schematic showing counterbalanced 

 internal left spiral grain (A) and external 

 right spiral grain (B) . Such a pole would be 

 able to resist the tendency to twist and would 

 remain straight in service. 



Interpretation of Studies 



These studies have pointed up several practical considerations concerning spired grain and 

 twisting in poles: 



1 . They have emphasized again that spiral grain is the normal growth pattern in trees 

 and that grain in young trees tends to spiral to the left, to straighten out as the tree grows older, 

 and finally tends to spiral to the right. 



2. No method of detecting spiral grain was found in live trees or unpeeled poles by means 

 of surface characteristics. 



3. Direction and slope of grain may be correlated to some extent with growth rate. Spi- 

 rality to the left tends to be associated with fast growth and to the right with slow growth. Since 

 this is true, slope of grain may be controlled to some extent by silvicultural manipulation of 

 stand density. However, correlation of grain angle with growth rate needs further investigation. 



4. Twisting of poles in service was definitely correlated with spiral grain. Poles with 

 severe left-hand spiral tended to be the bad twisters. Poles with right-hand spiral usually were 

 more stable, with respect to twisting, than straight -grained poles. The cause of this difference 

 was determined to be the internal grain structure. Poles with surface left-hand spiral contained 

 left-hand spiraled grain from the center of the pole out to the surface. Poles with surface right- 

 hand spiraled grain usually contained left-hand spiraled grain near the pith and right-hand 

 spiraled grain near the surface. The result was counteracting twist forces and little net twist. 



5. Proper seasoning might stabilize poles having severe left-hand spiral and make them 

 satisfactory for use in pole lines . 



6. Spiral grain specifications for poles need to be revised. 



13 



