399 
Groom .—* Brown Oak' and its Origin . 
possessed a thick internal layer of the wall that assumed a faint lilac tint 
with iodine, a blue colour with iodized chloride of zinc, and refused to 
answer tests for lignified walls. The occurrence of this wall-layer in the 
sap-wood proves that in the ‘ brown oak 5 its lack of lignification is not due to 
fungal attack. 
(b) Normal heart-wood. 
The heart-wood near the sap-wood differed from this by the almost 
complete lack of starch (remnants of which occurred in isolated ray-cells 
and in thyloses of the large vessels), and by the abundance of tannin 
not only in all kinds of parenchyma, but also in the walls of the con¬ 
stituents, especially the fibro-tracheides, thyloses, and to a less extent ray- 
parenchyma. 
(c) Brown heart-wood. 
The ‘ brown oak ’ showed the same general distribution of tannin as in 
the normal heart-wood. But it also contained not only solid, including 
brown, substances in various constituents of the wood, but also hyphae. 
For the purpose of cutting sections, the wood was softened by treat¬ 
ment with 50 per cent, commercial hydrofluoric acid (after being boiled and 
cooled repeatedly in water) and the wood blocks were eventually kept in 
a solution of glycerine, alcohol, and water. The sections were further 
treated with water if mounted in glycerine jelly, and, if mounted in Canada 
balsam, were for a time immersed in absolute alcohol and xylol. 
After such drastic treatment normal heart-wood had almost or entirely 
lost its tannin, and showed no solid nor coloured contents. ‘Brown oak’, 
on the contrary, even in its incipient stage still showed tannin in its walls 
and in certain solid brown bodies that occurred in various structural con¬ 
stituents. These brown bodies agree in reactions with the so-called ‘wood- 
gum ’ or ‘ wound-gum 5 of wood. 
1. The substance is insoluble, and does not swell appreciably in water, 
alcohol, xylol, concentrated hydrochloric acid (12 hours), concentrated 
sulphuric acid (12 hours), equal parts of concentrated ammonia and caustic 
potash solution (12 hours), nor successively in the last named and strong 
hydrochloric acid. (In the case of brown oak that had reached its final 
condition and was treated with concentrated sulphuric acid, there seemed to 
emerge from the brown bodies in question bubble-like drops of a colourless 
substance. These drops were probably derived from fungal hyphae con¬ 
cealed within the brown substance.) 
2. With phloroglucin and hydrochloric acid the brown substance some¬ 
times assumed a carmine colour and thus agreed with typical wood-gum, 
but even in such cases it refused to respond to Maule’s test for lignification ; 
in other cases it remained yellow with phloroglucin and hydrochloric acid. 
Possibly the substance is never lignified, and owes its occasional response to 
