398 Groom .—‘ Brown Oak' and its Origin . 
kept upright, and in some cases the plugs of cotton-wool were covered with 
caps of tin-foil. At the bottom of the tube was previously sterilized water 
containing spores that had not adhered to any of the blocks. This arrange¬ 
ment ensured to the different blocks different degrees of moisture, the 
supply of moisture increasing from above downwards, the lowest block 
being permanently partly immersed in water. 
The blocks in the middle of each column in the tube had the medium 
amount of moisture, and it was they that assumed a brown colour similar 
to that of c brown oak ’ (in fact very similar to Messrs. Oliver’s specimen), 
but varying towards that of fumed oak. The blocks partly immersed in 
water, and those at the top of the column in tubes, when no tin-foil caps were 
used, showed little or no change in tint. The brown colour was assumed 
therefore only when the heart-wood contained moisture exceeding a certain 
minimum , and falling short of a certain maximum. Such is one of the 
conditions of development in wood of all wood-destroying fungi. 
In a second series of cultures in which larger boards of heart-wood 
were used, and the precautions against the intrusion of foreign organisms 
were less rigid, the boards showed the successive characteristic changes of 
tint from yellow to brown, including small patches of the rich brown of 
genuine ‘ brown oak \ 
Distribution of the mycelium in the wood of the tree. 
The colour of the hyphae emerging in culture from browning oak, the 
definite localization of these emerging hyphae, and the artificial production 
from heart-wood of wood simulating ‘ brown oak all point to a causal 
connexion between fungus and browning process. This view is strengthened 
by the distribution and nature of the mycelium in the wood of the standing 
tree. Hyphae are absent from the sap-wood (and tissue outside it), and 
from parts of the normal heart-wood distant from the brown wood; they 
occur in an active living condition in regions of the heart-wood where 
conversion into brown wood is taking place, and, lastly, are present, mainly 
at least, in a dead and disguised form in ‘ brown oak 5 that has attained its 
final yet firm condition. The fact that in the mature brown oak the 
mycelium is wholly, or possibly nearly wholly, dead causes one to doubt if 
the decay observed in * brown oak ’ is due to the same fungus ; and 
additional reasons for this doubt will be given later in this paper. 
Structure and Development of ‘Brown Oak’. 
(a) Sap-wood. 
The structure and contents of the sap-wood are normal; starch was 
particularly abundant in the parenchyma, thyloses, and medullary rays. 
In the sap-wood, normal and brown heart-wood, many fibro-tracheides 
