404 Groom .—‘ Brown Oak ? and its Origin. 
Several sets of facts favour the view that tannin is used as food- 
material. 
i. An analysis of ‘ brown oak * compared with the normal heart-wood 
showed that the latter contained 13-33 and the former 10-05 per cent, of 
tannin. This would represent a loss of nearly 25 per cent, of the original 
tannin. But in the absence of analyses of oak timber at different depths 
inwards in ordinary heart-wood, it is conceivable that the smaller amount in 
the brown oak is not due to the fungus nor associated with the * browning \ 
1 . The distribution of the fungus and tannin are of significance in this 
connexion. (For purposes of observation the wood was softened by dilute 
glycerine, induced to enter by means of an exhausting air-pump: no heat 
was applied.) 
In the fully brown heart-wood tannin was generally diffused in the 
lignified walls, but especially in the lumina of the wood-parenchyma, 
thyloses, and cells of the medullary rays. In all uniseriate and multiseriate 
rays there was tannin, which often was most abundant in the marginal cells 
and lacking from many other cells. It was in all three forms of parenchyma 
that the hyphae and brown substance were also most abundant. In one 
and the same cell frequently parts of the brown substance contained tannin, 
which was absent from other parts of the same mass in the same cell. 
In regions where conversion of the heart-wood into ‘ brown-oak ’ was 
taking place some of the cells of the wood-parenchyma and medullary rays 
were poor in tannin, or devoid of it, and at the same time free from 
hyphae; whereas contiguous cells in the same tangential or radial series 
contained hyphae and richer stores of tannin. Again, in some cells there 
was no tannin except a thin film in (or on ?) the hyphal wall, or isolated 
minute droplets studding the hypha, which sometimes also traversed 
a larger globule of tannin: in these cases the tannin stained unusually 
light blue (a somewhat dark cobalt-blue) with ferrous sulphate, yet was 
sufficiently concentrated to stain deeply with lactic blue. 
These facts are all capable of two opposed interpretations, namely that 
the hyphae consume or excrete tannin. The view more consistent with 
evidence derived from other sources is that the hyphae preferentially enter 
tannin-containing cells, and consume the tannin until in the absence of fresh 
supplies tannin is so reduced in quantity as to be a dilute solution in the form 
of a film or minute globules on the hypha. After that stage the tannin 
may be wholly absorbed. But in addition to the tannin present in the cells, 
there is that in the walls ; this may be liberated from the wall by the solution 
of some ingredients in the wall or by water or a solution excreted by the 
fungus, and may be deposited in the accumulating brown substance. 
This view that the fungus feeds at the expense of the tannin is 
strengthened by cultures made of the fungus in soliUions of tannin. Coni- 
dia of the fungus were sown in 0-05,0*25,0*5 per cent, solutions of commercial 
