TIMBER 



11 



from the centre of the tree, one sometimes finds several 

 more rings on the same space on one side than on the 

 other. The rings are sometimes found contorted, due to the 

 action of winds, and in some trees are wavy in outline, as 

 in some of the oaks. In oaks and other hardwoods the 

 dark shaded portion which forms the patterns on boards 

 is the spring wood and the lighter portion the summer 

 wood, just the contrary to what it 

 is in pine. 



Many of the tropical trees show 

 clearly distinct rings, and in 

 others, such as greenheart, the 

 rings are clearly defined in one 

 part and in other parts appear to 

 blend into each other, forming 

 dark undefined bands. In these 

 tropical woods there is no time 

 of the " fall of the leaf," as in 

 conifers and other timber of the 

 northern hemisphere, so the 

 annual rings are not generally so 

 clearly defined. 



Wood is called " coarse grained " 

 or of " bigger bait " if the annual 

 rings are wide apart, and " fine grained " if they are close. 



FIG. 3. Block of Oak. 

 0. S., cross section ; R. S. 

 radial section ; T. S. 

 tangential section ; m. r. 

 medullary rays ; a 

 height ; b, width ; e 



length of med. 

 (After Roth.) 



ray. 



Shrinkage of Timber. Looking at the cross section of a 

 piece of ordinary hardwood with a magnifying glass it 

 appears exactly like a web of cloth or spider's web, with 

 the annual rings in one direction and the medullary 

 rays crossing them at right angles and connecting them 

 together. The medullary rays, which are always present, 

 even when the annual rings are absent, though sometimes 

 so fine as to be invisible, except with the microscope, 



