12 
TIMBER 
generally appear in cross section as hard, thin bands, 
and in some cases they are an inch deep on the vertical 
section, Figs. 3 and 5. The sj^aces between are filled to a 
greater or less extent by what look like small pinholes 
running longitudinally through the wood in circular lines, 
and form the annual rings ; these pores are very conspicuous 
in most woods except conifers. The web-like arrangement 
is very noticeable in hickory, where the concentric and 
radiating lines are clearly marked (Fig. 4). 
These tubes or cells or pores, as they are generally 
called, appear circular 
in section to the naked 
eye, but they are 
various sided figures, 
from a parallelogram to 
nearly a circle, and 
when cut through 
longitudinally, as in 
planing wood, show as 
channels or indenta- 
tions on the surface and 
form the "grain" of 
wood. The so-called 
pores are cells or tubes, enclosed by walls of cellulose, 
which, with other material, forms the fibres of the wood. The 
tubes are not continuous, each one is distinct from the 
other, and they are closed at the ends. Their length is 
from to of an inch, and is from fifty to one 
hundred times greater than their breadth. After a certain 
amount of moisture has been extracted from the timber 
these cell walls begin to shrink ; but, as has been said, 
their length being very much greater than their width, 
although shrinking may take place in both directions, it is 
not appreciable in the long diameter of the cells, and as 
