OBSERVATIONS ON CANADIAN CONIFEE^. 25 



In Piiius albicauUs it has been shown that tlie summer wood is thin and inconspitnnjiis, 

 while in Pinus imnderosa it is also thin but somewhat jn-ominent. In neithei- of these cases, 

 however, is it so prominent or dark as to suggest a special deposit of resin in the form of 

 plates. Moreover, as also shown, the fractures established in the woods by seasoning are 

 almost wholly radial and determined, both in position and direction, by the medullary rays, 

 while there are tangential fractures which depend for their direction and origin upon the 

 special qualities of the summer wood, or upon the diiferences in structural value between 

 the spiring and summer woods. It is, therefore, clear that with respect to- the formation of 

 resin-plates and their influence upon breaking up of the timber in seasoning, these two 

 species may be wholly ruled out of further consideration. 



In Pseudotsuga douglasii it has been shown that the summer wood is hard, flinty, pro- 

 minent and resinous. In the Kootanie specimens, as in several others of the coarse-grained 

 variety from other localities, it may also be observed that the action of the saw leaves the 

 dense summer wood in the form of prominent ridges. 



The tendency to radial fracture, independently of the medullary rays, as determined by 

 separation of the summer tracheids along the line of the primary cell wall, and to tangential 

 fracture, as determined either by the same cause or more frequently by rupture of the thin- 

 walled spring tracheids along the outer face of the dense and resisting summer wood, is 

 common to all the coarse-grained specimens, of which a number have been brought under 

 examination. It is, therefore, by no means a peculiar feature of the Kootanie specimens. 



In Lariz occidentalis it has likewise been shown that the summer wood is thick, dense, 

 dark and resinous, but the structure as a whole is compact, and the saw leaves a smooth, 

 even surface. The very strong tendency to rapidly develop in(kqiendent and irregular tan- 

 gential and radial fractures, either in sawing or under the action of the hatchet or chisel, is, 

 I believe, a peculiar feature of the Kootanie representatives of this species ; but this view is 

 expressed with reservation, as I liave not had an opportunity of examining specimens of 

 large size from other localities and under similar conditions of treatment. But that this 

 splitting-up is in no way connected with the local or excessive deposit of resin has already 

 been made clear. 



In both Pseudotsiiga and Lavlr the peculiar prominence of the summer wood, and in 

 the former particularly, the character and direction of the associated fractures, are such as 

 to suggest the occurrence of plates of resin and tJieir intlucnee upon the breaking up of the 

 structure in seasoning. To this, therefore, we must attribute tlie statement brought to our 

 attention in the first instance. 



The peculiar fractures in Pseadotsuga and Lanx call for special explanation. In Pscudo- 

 tsaga the tangential fracture along the outer face of the dense summer wood is clearly refer- 

 able to the apposition of tissues of widely different structural characteristics, and therefore 

 possessing very different degrees of resistance to mechanical stress. It is in this case not a 

 question of organic weakness, for the degree of cohesion is complete, but one of structural 

 weakness. (See fig. 1, plate III.) 



In both Pseudotsuga and Larix the fracture established taiigentially and radially through 

 the summer wood between rows of tracheids, is of the same nature, and may l)e referred to 

 the same cause. 



Sec. III., 1894. 4. 



