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, Moliseh, and 

 Moeller. They all regard the coloured materials as being 

 singular in chemical constitution, and the terms " gam " 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 



lie matter... 77-84 



Ash ... 7-80 



100-00 



Per cent. 



Water extract (soluble 

 gum) ... 3-60 



5 per cent. NaOH ex- 

 tract ... 7-24 



Eesidue (dark rods) ... 67-00 



Ash in residue ... 7-02 



Mr. Bamber finds that the 5 per cent, caustic soda solution 

 contains a gum precipitable by alcohol, and a resinous body, 



