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 of 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. 
