OBSERVATIONS ON CANADIAN CONIFEE.E. 



41 



From the foregoing results we may draw the following conclusions : 



1. The development of shakes is dependent upon organic peeuliariticR ht the cell wall 

 and not upon structural ditterences. 



2. The susceptibility to fracture is determined by climatic conditions as' influencing the 

 organization of the cell wall, particularly with respect to the elements of wafer. 



3. The resistance which this wood offers to transverse strain, is probably directly related 

 to the relative predominance of the summer wood. 



4. The weight per cubic foot probably increases with an increase in volume of the 

 summer wootl. 



EXPLANATION OF PLATES 



J 'late I. 



lUuslratinp; structural flitrerences in Kootanie woods, x HO. 



Fig. 1. Pseurlotsugi douglasii, from the Kootanie Valley, B.C. 



" 2. Pseiirlot-iu »a douglasii, " tine-grain," from t'le Sargent collection. 



" :{. P.-ieudotsuga douglasii, " fine-grain," from the Sargent collection. 



" 4. Larix occidentalis, from the Kootanie Valley, B.C. 



" 5. Pinu.s albicaulis, from the Kootanie V^alley, B.C. 



" (i. Pinus ponderosa, from the Kootanie Valley, B.C. 



Plate II. 



Illustrating structural variations in ]'seudots\iga douglasii. x Cid. 



Fig. 



Plate III. 



PsrudoffiKgri rhmglasii. 



Fig 1. Transverse section showing character of fracture along the outer face of the .summer wood, x 36. 

 " 2. Transverse section showing character of rupture in the spring wood under mechanical stress, x 'MS. 

 " 3. Transverse section from specimen 783, showing the character of the structure and nature of a 



wind shake, x 36. 

 " 4. Transverse section of fine-grained wood, x 36. 



Plate IV. 



Pscudotsuga flouglasii. 



Fig. 1. Transverse section of 35a showing the character of structure of coarsegrained wood, x 36. 

 " 2. Transverse section showing character of fine-grained wood from the same tree as the preceding— 



a56. X 36. 

 " 3. Photograph of a timber showing character of the fracture in longitudinal shear under mechani- 

 cal stress. 



Sec III., 1894. 6. 



