122 



PROPERTIES OF WOOD. 



transformation of sapwood into heartwood is somewhat as 

 follows : 



Thus the conversion of sapwood into heartwood proceeds 

 irregularly, and not according to the annual zones. At first 

 the percentage of sapwood is enormous ; later on the difference 

 between the volume of new sapwood formed and that of the 

 old sapwood transformed into heartwood steadily diminishes, 

 until between 90 to 100 years equal volumes of heartwood 

 and sapwood are formed annually. 



Oaks with rapid growth and with smooth bark have com- 

 paratively more sapwood than slower growing trees with 

 rough bark, and those grown on north and east slopes have 

 more sapwood than those grown on south and west slopes. 

 Pedunculate oaks usually have more sapwood (2 8 C.) than 

 sessile oaks (1 5 C.). 



In the case of oaks grown in high forest the conversion 

 of sapwood into heartwood begins later, and is the earlier 

 and the more active, the more light is given to the 

 poles. Suppressed oaks often have no heartwood when 

 25 years old, while old high forest trees have more zones 

 of s;i|)\von(l (18 25) than old standards over coppice. 

 Oaks coming from the last thinnings have little sap- 

 wood. 



Stunted oaks grown on impermeable London clay at 

 Oxshott, in Surrey, have little sapwood and produce very 

 hard wood, suitable for gate-posts. Tr.] 



