PENETRATION AND DECAY 



365 



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Fijr. 2— The increment borer. The central figure shows the borer assembled. 

 At the left are the extractor, the hollow boring tube, and the handle. Four increment 

 borer cores are shown at the right. 



and find favorable conditions for growth in untreated, non-durable 

 sapwood lying beneath the treated outer layers of wood. Cross sec- 

 tions of poles showing internal decay of the untreated sapwood are 

 shown in Fig 1. 



A systematic inspection of 3102 poles in the selected lines was made 

 by one of the authors, Mr. C. H. Amadon. The possible variances 

 that might arise from different personal methods and interpretations 

 were therefore minimized as far as practicable. Each pole was first 

 tested by sounding with a hammer or a hatchet. When the hammer 

 blows produced a dull lifeless tone, suggesting a hollow or decaying 



