DOUGLAS FIR FIBER, 

 WITH SPECIAL REFERENCE TO LENGTH 



By H. N. Lee/ A.M., and E. M. Smith^ 



Sanio in 1867 investigated (6) the variation in size of the 

 tracheids in Scotch pine {Pinus sylvestris L.), and deduced five 

 general laws : 



1. In the cross-section of a stem or branch the tracheids in- 

 crease in size for a certain number of annual rings from the pith 

 until a maximum is reached, after which the size remains 

 constant. 



2. The final constant size in the stem varies at different dis- 

 tances from the ground, first increasing till a maximum is reached 

 and then decreasing toward the top. 



(a) The tracheids in a given annual ring increase in size from 

 the ground upwards until a certain maximum is reached and then 

 decrease toward the top. 



The other laws have to do with the fibers of the branches and 

 roots. 



As a result of their study on pine, fir, spruce and hemlock, 

 Shepard and Bailey (/ and 2), reach the following conclusions: 



1. No constant maximum length of tracheids occurs. 



(a) The length rapidly increases, in a given cross-section of 

 the stem, for the first 25 to 50 years, then there is a marked de- 

 crease in length for about a decade which in turn is followed by 

 an increase. In the only old material studied there was a maxi- 

 mum at 160 years followed by a comparatively rapid decrease. 



2. Sanio's second law holds for Picea rubra. 



(a) The maximimi tracheid length occurs higher from the ground 

 in rings nearer the bark. 



3. There is no relation between the width of annual ring and 

 the length of the tracheids. 



4. The tracheids in "rotholz" are shorter than those in "sug- 

 holz" of the same annual ring. 



5. There is so much variation in the length of tracheids that this 

 feature is not a safe method to use in identification of wood. 



After an extended study on White pine. Loblolly pine, Long- 



^ Forest Products Laboratories of Canada. 



671 



