Trees — The Character, Structure, Sec. 49 



had experience in chopping wood, knows that it is easier to 

 cut radially than tangentially, or when directed slantingly 

 across the grain. This means that the elements normally run 

 parallel to the trunk, and any \'ariation from this straight-grained 

 character would have a detrimental effect on the strength when 

 used as structural timber. Spiral grain means that the fibres 

 run abnormally in an oblique direction instead of vertically, and 

 if split would show a twisted, fluted surface. It is generally 

 indicated by the twistings of the bark. Softwoods appear to be 

 more subject to spiral grain than hardwoods. It sometimes 

 happens, for instance, in old trees of Tamarack, a species of 

 Larch, {Larix laricina) that the inner wood is straight-grained 

 while surrounded by an outer layer of spiral grain several inches 

 thick. 



The tenacity of wood when strained "along the grain" 

 depends upon the tenacity of the walls of the fibres ; when 

 strained across the grain" it depends upon the lateral adhesion 

 of the sides of the fibres to each other. In softwoods, adhesion of 

 the fibres is small, so that they are more easily split "along the 

 grain " or torn across the fibres than in hardwoods. 



Softwoods. (Pines, Firs, Larches, etc.). 



In softwoods we find the simplest type of tissue. It is this 

 simple and regular structure which enables softwoods to be more 

 easily worked and seasoned than hardwoods. 



Tracheids. — It is this element which practically makes up 

 the wood of softwoods. They ai-e tiny elongated fibre-like cells 

 of varying length, thin walled, and spindle shaped, the tapering 

 ends "breaking-joint" with each other. On the walls are 

 numerous bordered pits arranged in vertical rows that appear in 

 section under the microscope as double concentric rings. They 

 form double valves to regulate the distribution of water. 



Wood-Cells {Wood parenchyma). — These are thin-walled 

 isometric cells forming a soft tissue, and are only scantily scattered 

 in softwoods, among the tracheids, as in Junipers. In some 



