405 
Groom .—‘ Brown Oak’ and its Origin . 
tannin (which is not identical with the tannin of oak wood). When bacteria 
were excluded vigorous submerged mycelia developed, but the solutions did 
not darken in tint. When the mycelia were accompanied by bacteria, 
derived from cultures from the original wood, the solutions darkened. 
Inside ‘ brown oak ’ I failed to find any bacteria. 
Identity of the Fungus. 
Repeated trials as to the source of the Penicillium -like conidiophores 
emerging from incipient ‘brown oak’ showed that these belonged to the 
fungus causing the process of browning. This was confirmed not only by 
the physiological action of the mycelia in cultures made in oak heart-wood, 
but also by the occurrence of minute P enicillium-Xike. conidiophores in the 
narrow vessels of the intact ‘ brown oak \ 
As regards other stages of the life-history of the fungus, I did not 
succeed in obtaining by means of cultures derived from conidial infections 
any other stage. But from the regions where the hyphae were still active 
on samples of the ‘ brown oak ’ from England and Scotland there were 
produced little spheroidal brownish-yellow fructifications, whose diameter 
did not exceed that of half a pea-seed. These appeared to belong to the 
Plectobasidiinae. Being unable to identify these, I submitted them to 
Mr. George Massee, who states that they are the basidiocarps of Melanogaster 
variegatus , Tul., var. broomianus , Berk. 
Summary. 
In certain individual British oak-trees (Quercus Robur x ) the ordinary 
heart-wood is partially replaced by a rich-toned, often reddish, brown wood, 
which is firm and hard, and is termed ‘ brown oak \ 
Under the influence of a septate fungus living exclusively in the heart- 
wood normal heart-wood is changed in ‘ brown oak ’. The fungus therefore 
presumably infects solely, through a wound, trees sufficiently old to possess 
heart-wood. 
‘ Brown oak’ usually occurs at the base of the trunk and the adjoining 
root, and generally tapers upwards in the stem and downwards in the root. 
But the fungus can gain entrance to upper parts of the tree and so produce 
in these regions masses of ‘ brown oak ’, even in individuals devoid of it in 
their lower parts. 
The fungus in the infected tissue is responsible for the production of 
a brown substance (or brown substances) highly resistant to solvents and 
responding to the reactions of the ill-defined material termed 4 wound-gum ’ 
or ‘ wood-gum \ This arises in the form of colourless or faintly yellow 
globules or granules, which eventually aggregate to form brown masses in 
1 This name is used in its main historic sense as including Q. pedunculata and Q. sessiliflora. 
From which of these species my material was derived, and the extent to which ‘ brown oak ’ occurs 
in the two, are unknown to me. 
