* Brown Oak’ and its Origin. 
BY 
PERCY GROOM, M.A., D.Sc., 
Professor of the Technology of Woods and Fibres, Imperial College, London . 
HE ordinary heart-wood of certain individual trees of Quercus Robur in 
Great Britain is sometimes partially replaced by a firm, richer-toned, 
often reddish, brown wood known as * brown oak ’ or £ red oak Such 
wood varies in tint from dull brown to rusty brown, or even to rust-coloured. 
Sometimes it is uniformly coloured, but at other times longitudinal bands 
of more or less normal-coloured heart-wood alternate with deep or bright 
brown streaks, which may include nearly black patches. This latter type 
of ‘ brown oak ’ is the so-called ‘ tortoiseshell ’ variety. 
Trees possessing £ brown oak ’, so far as is known, show no external 
differences from normal individuals. This is not surprising as the heart- 
wood is the sole part affected, the remaining tissues being normal in structure 
and apparently in dimensions. In particular the sap-wood seems to be of 
ordinary size, and the sole evidence suggesting a possible precocious con¬ 
version of sap-wood into heart-wood is limited to the occasional presence 
of scanty starch-grains in a few cells of medullary rays in the heart-wood. 
Some £ brown-oak ’ trees are stag-headed. This condition induced by the 
desiccation of the branches is known to be caused by a number of influences 
that either check the supply of water to the foliage, or induce excessive 
transpiration. The evidence provided later in this paper proves that there 
is no reason to believe that the stag-headed condition of £ brown-oak ’ trees 
is directly induced by the influence responsible for the production of the 
brown heart-wood. 
General Distribution of ‘Brown’ Wood . 1 
In the trunk the brown wood most frequently occurs at the base, 
extends upwards to a variable height, and usually tapers in such a manner 
that its topmost portion apparently coincides with the inmost heart-wood. 
Not infrequently, however, in its upward taper the ‘brown heart ’ becomes 
gradually confined to one side of the trunk. A special example of this was 
1 For many of the facts concerning the general distribution of ‘ brown oak 5 in the individual tree 
I am indebted to Messrs. Alexander Howard and Stuart Oliver,the former of whom informs me that 
he has seen * brown oak ’ in a specimen of Quercus rubra . 
[Annals of Botany, Vol. XXIX. No. CXV. July, 1915.I 
D d 
