136 THE OAK 



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 greyish or yellow brown (fawn colour) 

 to reddish or very dark brown. It darkens on expo- 

 sure, and works to glossy surface if healthy. 



Annual rings well marked by the one to four lines 

 of large vessels in the spring wood, whence radiate out- 

 wards tongue-like and branched groups of smaller and 

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

 darker fibres. Indistinct peripheral lines of parenchyma 

 are also visible, especially in the broader annual rings. 

 The annual rings are slightly undulating, bending out- 

 wards between the large medullary rays (fig. 38). 



