OBSERVATIONS ON CANADIAN CONIFEE.E. 



37 



tions commonly met with. Section 4 exhibits the general features of the " yellow " or " fine- 

 grained " variety as derived from specimen 'So. 2. From this, one may gain a very good 

 conception of the structural features which characterize the l)est (piality of this wood. Sec- 

 tion No. 1 was taken from specimen ISTo. 316, and well shows not only the coarse-grained 

 character of the red variety, but its tendency to fracture freely in an irregular mannei*. Sec- 

 tions 2 and 3 were derived from the Sargent collection of North American woods, and were 

 marked " coarse-grained " and " fine-grained " respectively. The sections, however, show 

 no material difference. They are introduced here in order to show the extreme of reduction 

 in the dimensions of the growth-rings and volume of the summer wood, which has been 

 carried so far as to destroy all resemblance to the other specimens. The contrast is made 

 most striking by comparison with fig. 1, plate II. 



The relative volumes of the spring and summer woods show well-marked variations 

 which have an important bearing upon the strength of material, and also upon the weight 

 of the wood. Comparison of figs. 1-8, plate I., and figs. 1-6, plate II., will make this 

 apparent. 



In the Kootanie wood (fig. 1, plate I.) the summer wood is about one-fourth the spring 

 wood. In the specimens derived from bridges and other structures in British Columbia, 

 considerable variation is to be noted, while in the two specimens from the Sargent collection, 

 it appears that the summer wood is often reduced to a narrow line of structure only one or 

 two tracheids wide, which cannot bo represented on the scale to which these figures are 

 drawn (figs. 2 and 3, plate I.). These variations will be best appreciated by means of a 

 tal)ulation : 



No. V. 



RELATIVE VOLUMES OF SPRING AND SUMMER WOODS. 



From this it appears that No. 2 representing the highest grade, and No. 316 representino- 

 the lowest grade of this timber, stand at opposite extremities of a graduated scale. From 

 this the inference might be drawn that the value of Douglas fir for structural purposes, and 

 its freedom from shaking and longitudinal shear is directly related to the relative volumes of 

 the summer and spring woods in such a way that the lower the ratio, or the greater the ten- 

 dency to equality between these two parts of the structure, the higher does the value become. 



