50 WRIGHT : THE GENUS DIOSPYROS 



The durability of our Diospyros timbers is due to the 

 nature and percentage number of the elements comprising 

 the wood, together with the presence of coloured contents 

 partially or wholly filling the elements. In all our Ceylon 

 species of Diospyros the cambium divides very slowly, and 

 the elements, particularly the fibres, possess small transverse 

 dimensions and thick walls ; the percentage number of fibres 

 is in every case very high, and that of the tracheal elements 

 very low, consequently the xylem is much more durable 

 than the majority of our Ceylon timbers. Nevertheless, the 

 histological composition of the secondary xylem is only one 

 factor in determining the durability of these timbers, the 

 infiltrated gums and resin providing a substantial support to 

 the otherwise empty elements. The relative durability of 

 the outer white sapwood and the central ebony is well seen 

 in trunks of trees exposed to the atmosphere and vermin ; 

 the sapwood is stripped completely in a few years, leaving 

 a smooth black log of ebony which resists the attacks of ants 

 and many wood borers. 



Discolouration off Timber. 



The discolouration of the wood is mainly due to chemical 

 and physical changes of the materials stored in the elements 

 of the wood, and to a less extent to a change in composition 

 and colour of the cell walls. The coloured material entirely 

 fills the lumina of the elements in pure ebony, and 

 decreases in quantity as one passes to the red, yellow, and 

 white woods. The white sapwood surrounding the central 

 ebony contains a varying quantity of coloured material 

 partially filling the secondary elements, and the quantity of 

 this material increases from without inwards. 



To the naked eye there appears to be a sharp distinction 

 between the limit of the central ebony and the white 

 sapwood. A gradual series of changes can, however, be 

 discerned in microscopic sections, and for the conversion 

 of the peripheral sapwood into ebony it is mainly a question 

 of time. 



