20 



TIMBER. 



and also by fine wavy concentric lines of short, thin- walled cells (see 

 fig. 8 A), consists of thick-walled fibers (see fig. 8 B) and is the chief 

 element of strength in oak wood. In good white oak it forms one-half 

 and more of the wood; it cuts like horn, and the cut surface is shiny 

 and of a deep chocolate-brown color. In very narrow-ringed wood 

 and in inferior red oak it is usually much reduced in quantity as 

 well as quality. 



The pith rays of the oak, unlike those of coniferous woods, are 

 at least in part very large and conspicuous (see fig. 6, their height 

 indicated by the letter a, and their width by the letter b). The 

 large medullary rays of oak are often twenty and more cells wide 

 and several hundred cell rows in height, which amount com- 

 monly to one or more inches. These 

 large rays are conspicuous on all sec- 

 tions. They appear as long, sharp, 

 grayish lines on the cross section, as 

 short, thick lines, tapering at each 

 end, on the tangential or "bastard" 

 face, and as broad, shiny bands, the 

 "mirrors," on the radial section. In 

 addition to these coarse rays, there is 

 also a large number of small pith 

 rays, which can be seen only when 



magnified. On the whole, the pith ''f\\ v= | =| \\\ 



rays form a much larger part of the vy| 

 wood than might be supposed. In 

 specimens of good white oak it has 

 been found that they formed about 

 16 to 25 per cent of the wood. 



MINUTE STRUCTURE. 



a 



If a well-smoothed, thin disk, or 

 cross section of oak (say one-sixteenth 

 inch thick) is held up to the light, it 

 looks very much like a sieve, the 

 pores or vessels appearing as clean- 

 cut holes; the spring wood and gray 

 patches are seen to be quite por- 

 ous, but the firm bodies of fibers 

 between them are dense and opaque. 

 Examined with the magnifier it 

 will be noticed that there is no such regularity of arrangement in 

 straight rows as is conspicuous in the pine; on the contrary, great 

 irregularity prevails. At the same time, while the pores are as large 

 as pin holes, the cells of the denser wood, unlike those of pine wood, 



Fig. 9.— Isolated fibers and cells, a, four cells 

 of wood parenchyma; b, two cells from a 



" pith ray ; c, a single joint or cell of a vessel, 

 the openings x leading into its upper and 

 lower neighbors; d, tracheid; e, wood fiber 

 proper. 



