186 THE OAK 
CHAPTER X 
OAK TIMBER—ITS STRUCTURE AND TECHNOLOGICAL 
PECULIARITIES 
Ir 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). 
