PSEUDOTSUGA 



273 



4. The size of the tracheids and the volume of the lumen vary rela- 

 tively to the total area of the cross section, whereby in some cases the 

 summer wood presents a very dense structure, while in others it is com- 

 paratively open. The extreme variations observed in nine specimens from 

 different localities lie within the following limits : 



Spring wood 24x43^-43x77^ 



Summer wood 18 x 27 /j. 26 x 53 /x, 



A large tree 61-92 m. high, with a trunk upwards of 3.66 m. in diameter. 



Wood hard, strong, varying greatly with age and conditions of growth, 

 difficult to work, very durable (Sargent). 



Two varieties are recognized : the " yellow fir," distinguished by its lighter 

 color and usually fine and compact grain ; and the " red fir," which 

 approximates to the characteristics of the next species and is distin- 

 guished by its darker red color, coarse grain, and flinty summer wood. 

 The former is of superior quality for constructive purposes. The great 

 strength and durability of this wood make it the most valuable species 

 of the Pacific region, and it is largely employed where these qualities, 

 joined to great size of timber, are required. 



Relative specific gravity 



Percentage of ash residue 



Approximate relative fuel value 



Coefficient of elasticity in kilograms on millimeters 

 Ultimate transverse strength in kilograms 



0.5157 

 0.08 



51-53 

 1283. 



376. 



Ultimate resistance to longitudinal crushing in kilograms 8289. 

 Resistance to indentation to 1.27 mm. in kilograms . . 1608. 

 (Sargent) 



A comparison of these values with those given by Sargent for some of 

 the more commonly used oaks will serve to show the superior quality 

 of this timber, which has a higher coefficient of elasticity than our three 

 best native species. 



COMPARATIVE STRENGTH OF OAKS AND DOUGLAS FIR 



(After Sargent) 



