CHAPTER X. 



OAK TIMBER ITS STRUCTURE AND TECHNOLOGICAL 

 PECULIARITIES. 



IT is now time to look at the timber of the oak as a 

 material, and to examine its technical properties from 

 the various points of view of those who employ such 

 material. Oak timber may be described as follows : 



(1) Appearance and Structure. Pith pentangular, 

 1 to 4 mm. diameter, whitish at first, and then browner, 

 formed of small, thick-walled cells. 



Sap-wood narrow and yellowish-white ; heart-wood 

 varies in shades of grayish or yellow brown (fawn color) 

 to reddish or very dark brown. It darkens on exposure, 

 and works to a glossy surface if healthy. 



Annual rings well marked by the one to four lines of 

 large vessels in the spring wood, whence radiate outward 

 tongue-like and branched groups of smaller and smaller 

 vessels, tracheids, and cells, in a groundwork of darker 

 fibers. Indistinct peripheral lines of parenchyma are 

 also visible, especially in the broader annual rings. The 

 annual rings are slightly undulating, bending outward 

 between the large medullary rays (Fig. 38). 



