12 



TIMBEE 



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 spaces 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 



FIG. 4. Cross Section of Hickory. 



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 ^ l (T 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 



