158 THE OAK 
the wood by excreting soluble ferments which dissolve 
the substance of their walls, and feed on the products of 
solution. Hence they damage the timber in two ways 
—they riddle it through and through by myriads of 
minute apertures, and thus ruin its structure, and they 
Fia. 42.—Piece of oak destroyed by Thelephora Perdiz, 
showing the characteristic markings due to the action 
of the fungus. (R. Hartig.) 
reduce its substance by dissolving it and converting it 
to their own uses. The wood, therefore, loses in strength 
and in weight, and becomes ‘rotten.’ There are differ- 
ences in detail as to the mode of destroying the elements 
of the wood, but the final result is much the same in all 
