HEARTWOOD OF CRYTOMERIA JAPONICA 857 



This shows the chemical change undergone by the "particular 

 substance." 



The above statements and data, and the fact that the darkening is 

 easily removed with acid while the color reaction of the infusion, on 

 the other hand, is somewhat reversible with alkali and acid, are quite 

 enough to conclude that "particular substance" is at least one of the 

 direct factors causing this phenomenon. Here for convenience we call 

 the same substance the "chromogen of the darkening." 



It is now evident that the darkening is associated with chromogen 

 peculiar to "Sugi." Yet, the same chromogen is common to all kinds 

 of the heartwood of "Sugi" and therefore it can not be the sole factor, 

 as pieces of wood from one and the same tree or pieces equal in their 

 chromogen content are sometimes darkened and sometimes not dark- 

 ened. At least there ar.e remarkable differences in the appearance of 

 woods having equal amounts of chromogen. It is accordingly neces- 

 sary to take some other factor into account to secure a more satis- 

 factory explanation of this phenomenon. 



The darkening undergone by "red wood" when used under natural 

 wet conditions, or artificially produced by alkali, always corresponds 

 to some stage in the color conversion of "black wood." The dark 

 brown color in particular, identical with that of "black wood" in the 

 first stage of darkening, is obtained when green "red wood" is treated 

 with very dilute alkali. This color can be removed with acid as in 

 the case of "black wood." In both cases the tint is not only similar 

 but also subject to the same process of fading afterwards, through the 

 same stages of conversion, and culminates in grayish brown. While 

 the aqueous or the alcoholic extract of the wood or shavings, made 

 immediately after the darkening, is equally reddish like the basic in- 

 fusion of the woods, the extract of the wood in the advanced stage of 

 conversion is simply yellowish as that of the basic infusion of the 

 wood after long exposure to air or that of the same changed on the 

 application of acid. 



These facts lead to the consideration that the other factor may be 

 an hydroxyl group. The question may here arise as to the difference 

 in the color of the infusion and that of wood when treated with alkali. 

 The following facts seem to give an explanation : 



(I) The infusion immediately after the darkening of the wood is 

 red or purplish red. 



