Groom.—Brown Oak 9 and its Origin . 403 
(*) Action of the fungus on lignified walls. 
The effect of the fungus on the mechanical strength of the heart-wood 
is so small that ‘brown oak’ is an excellent material for panelling and 
furniture. This corresponds to the fact that the fungus attacks lignified 
walls as visible structures feebly and slowly. It appears to pass from one 
cell or vessel to another solely through the pits. This was particularly 
evident in the case of hyphae traversing the terminal walls of wood- 
parenchyma and ray-parenchyma; and cases were observed in which 
a hypha on reaching a spot on the wall where no pit occurred executed 
a bend and so reached the nearest pit. 
The constituents of the wood for the most part retain not merely their 
visible structural integrity but also their lignified condition. Yet the fungus 
has some power of delignifying wood. Here and there where two vessels, 
or a vessel and a tracheide, or two tracheides, were in lateral contact, the half 
of the wall belonging to the constituent containing hyphae gave a cellulose 
reaction in the vicinity of these, but a lignified reaction on the side towards 
the constituent devoid of fungi. In a more advanced stage of attack the 
wall was locally delignified throughout its thickness. This restricted power 
of delignification appears to begin at the pits, for the section of a wall 
separating two tracheae sometimes showed alternate minute patches of 
cellulose and lignified substance, each patch embracing the whole thickness 
of the wall. Each cellulose patch probably corresponded to a pit whose 
plane lay outside the section. Occasionally thin sections showed real 
gaps in the walls separating two vessels, although I never succeeded in 
proving beyond doubt that these were due to the fungus, and not to the 
razor. Probably owing to its weak power of attacking lignified walls, and 
its exclusive or nearly exclusive passage through pits, the fungus occurs very 
scantily in fibro-tracheides. 
(/) Source of nutriment of the fungus. 
As the fungus is confined to the heart-wood, and makes so slight an 
attack on the visible structure of the lignified walls, the question arises as to 
the source of its food. Available are: in the lignified walls, pentosans 
(xylan and so forth), pectic bodies, glucosides, and tannin, as well as the 
cellulose and substances causing the ‘lignin’ reactions. Tannin is also 
available in lumina of the parenchyma, including that of medullary rays, 
and thyloses. Whatever be the precise food substances utilized, the method 
of nutrition of this fungus is novel , so far as our present knowledge is con¬ 
cerned, though the future will probably reveal other wood-inhabiting fungi 
of similar feeding habits, possibly associated with the inception of firm 
wound-wood or firm false heart-wood, 1 
1 See E. Munch, 1 fiber krankhafte Kembildung \ Naturwiss. Zeitsch. f. Forst- und 
Landwirtschaft, 1910, Heft 11, 
