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 
w^ood, 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. 
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. 
Fig. 3.— Block of Oak. 
C. S., cross section ; E. S., 
radial section ; T. S., 
tangential section ; m. r. , 
medullary rays ; o, 
height ; h, width ; e, 
length of med. ray. 
(After Eoth.) 
