52 
WRIGHT : THE GENUS DIOSPYROS 
medullary ray cell to another, but the proportion of these 
elements is so small compared with the surrounding fibres, 
that any contents they may possess cannot greatly change 
the tint of the xylem as a whole. 
When the parenchymatous and tracheal elements have 
their lumina blocked the coloured material gradually 
infiltrates into the fibres. The coloured substances, under 
normal circumstances, first appear in the oldest elements, 
and therefore the blackening takes place from within out¬ 
wards. 
The composition and origin of the discolouring substances 
has been discussed by Belohonbek, Hartig, Molisch, and 
Moeller. They all regard the coloured materials as being- 
singular in chemical constitution, and the terms “ gum ” and 
“ resin ” have been frequently applied to the separated 
substances. 
The coloured substance is partially soluble in water, creo¬ 
sote, benzine, ether, and sulphuric acid. The solution varies 
in colour from a deep brown to claret red. In all cases 
microscopic examination of the sections so treated shows 
that only a very small proportion of the coloured substance 
has been extracted. If the sections are treated with strong 
sulphuric acid for several days the walls of the elements 
disappear and liberate long black rods of material which 
resist the attack of the strong acid even after heating. These 
black carbon-like rods appear to be unaffected after treatment 
with any reagent. Mr. Kelway Bamber has very kindly 
made an analysis of the coloured timber, and has allowed me 
to quote his results here : 
Ebony Dust. 
Per cent. 
Moisture 
14-36 
Organic matter... 
77*84 
Ash 
7-80 
100-00 
Per cent. 
Water extract (soluble 
gum) •• 3*60 
5 per cent. NaOH ex¬ 
tract ... 7‘24 
Residue (dark rods) ... 67‘00 
Ash in residue ... 7’02 
Mr. Bamber finds that the 5 per cent, caustic soda solution 
contains a gum précipitable by alcohol, and a resinous body, 
