48 
WRIGHT : THE GENUS DTOSRYROS 
uncertainty has long been recognized by persons engaged in 
financial speculations, and too much stress cannot be laid on 
the individual variation which occurs in trees of the same 
species from the same or different localities. 
On the other hand, there can be no question as to the 
specific tendencies to produce a definite type of heartwood, 
though even here one has to allow a wide range of vari¬ 
ability for each species. For instance, the heartwood of D. 
Melanoxylon and D. Ebenum is almost invariably jet black, 
and on this account these two species provide the greater 
part of ebony from India and Ceylon ; D. insignis, on the 
other hand, never yields a black heartwood, D. Gardneri 
always produces a yellow wood, and D. Moonii a timber 
which is of a red tint spotted here and there with small black 
strands. There could be no possible doubt of the species 
were the timbers of D. Ebenum, D. Kurzii, D. insignis, 
and D. quæsita to be mixed with one another, as their 
macroscopic characters are so pronounced. 
The specific colour tendencies are somewhat difficult to 
explain. The two factors which determine the colour of the 
timber in the respective species are : (1) the means of distribu¬ 
tion of the coloured substances ; (2) the proportion of coloured 
gum and resin present in the tissues. 
It is perhaps safe to assume that the best or most general 
distribution of coloured substances will be effected in those 
xylems the elements of which are freely communicating 
with one another, and therefore those species the timbers of 
which contain a high percentage of medullary ray cells and 
wood parenchyma should show the most general distribution 
of colouring substances. The fact that the xylem of D. 
insignis is highly parenchymatous and is really white points 
to the conclusion that for the production of ebony the 
superabundance of colouring material is the first desideratum, 
rather than profusely pitted elements. An open type of pit 
communication between the elements will tend to prevent 
the formation of central ebony in timbers where the colouring 
