396 Groom .— £ Brown Oak ’ and its Origin . 
that often it is found that ‘brown-oak’ trees have lost their tap-root, whose 
functions are carried on by massive lateral roots. 
Not one of these facts indicates definitely that the influence causing the 
rotting of the wood is identical with that causing the heart to become ‘ brown 
oak The facts merely indicate that in the case of these trees with rotten 
heart-wood, there are facilities for the entrance, through wounds, of fungi 
capable of attacking heart-wood of the oak, and that in certain cases those 
facilities are especially marked near the base of the trunk and roots. In 
the sequel it will be possible to discuss if the cause of browning and rotting 
of the wood is the same. 
Deepening in the colour of wood, such as is undergone by alder, or by 
the heart-wood of larch, pine, and other trees, on exposure to air and light 
is assumed to be of a purely chemical nature, and at least often is due to 
oxidation (which is also largely responsible for the change of tint in sap- 
wood that is being converted into heart-wood). But, with the exception of 
the still unexplained cases of the ‘ red heart ’ of beech and of French oak 
(Chine rouge), considerable deviations from the normal colour of the heart-wood 
are invariably due to the action of fungi. Yet no observer has recorded 
the presence of a fungus in firm ‘ brown oak 5 that shows no macroscopic 
symptoms of decay. And against the suggestion that a fungus or bacterium 
is responsible for the replacement of normal heart-wood by ‘brown oak’, is 
the fact that good ‘ brown oak ’ is to the timber-merchant or builder strong, 
hard, sound wood, responding to tools as does normal oak timber. It is true 
that species of Ceratostomella —for instance C. Pini —living in the sap-wood 
weakens the wood little or not at all, as its attack on wood-substance is 
slight; but in this case the fungus feeds on the carbohydrate and proteid 
food of the medullary rays and wood-parenchyma: such food is not generally 
available to any fungus living exclusively in heart-wood. 
Therefore there was no adequate reason for believing that ‘ brown oak ’ 
owes its origin indirectly to a fungus or other foreign organism, or is the 
first step in a process of decay. 
(3) The third hypothesis, namely that ‘brown-oak ’ trees are mere sports, 
can be dealt with only after the evidence supplied in the sequel. Yet it 
may be pointed out that on such a hypothesis the occasional uneven distribu¬ 
tion of ‘ brown oak * on the same site or in one and the same tree would 
find analogies in connexion with some tropical trees, including ebonies (e. g. 
Diospyros Kurzii and D. Melanoxylon ), whose true dark heart-wood shows 
similar varied development. 
True Cause of Production of ‘ Brown Oak 
As it seemed possible that the reason of our ignorance as to the cause ol 
the production of ‘ brown oak ’ lay in the lack of any microscopical observa¬ 
tions at the critical stage of its origin, I secured specimens of wood of freshly 
