SOME FUNGI IN WOOD.
31
tree, and may or may not continue their growth after the tree
has been felled; others appear in felled timber as it lies on the
forest floor, others again, like the dry rots, appear on prepared
timber.
Wood-inhibiting fungi fall into one of several groups,
according to the effect they produce upon the tree or timber.
The forester speaks of top rots, trunk rots, butt rots and root
rots, classifying wood-destroying fungi according to the position
in the tree, for this position is often remarkably constant, while
according to the symptoms they produce in the wood, the rots
are referred to as pocket rots, stringy rots, piped rots, cubical
rots and so on; such terms are more or less self explanatory.
The term dry rot refers to rot in prepared wood, while the timber
merchant refers to decay in timber as dote.
A useful general classification is into:—
Brown rots,
White rots,
Sap stains.
It was formerly thought that the brown rots were caused by
fungi, which fed upon the cellulose of the wood, leaving the
lignin as a brown residue, while the white rots attacked the
lignin and left the cellulose. Recent researches have shown
that this view is not entirely true. Thus Campbell [3] demon-
strated that in the white rot produced by Polystictus versicolor
the cellulose of the wood at first remains free from attack,
although the lignin and other wood substances are broken down;
in later stages of the decay, however, cellulose is broken down.
Again in Stereum hirsutum, a white pocket rot [4], he found that
both cellulose and lignin were decomposed, and even in the white
pockets which characterise this rot he found some lignin,
although it was formerly held that the whiteness of the decayed
wood in a white rot was due to the depletion of the lignin in the
wood. This investigator, however, found that there was a
chemical difference between the remains of the wood in some
white rots, as compared with some brown rots, since that of
the former became less soluble in 1% sodium hydroxide, as
decay advanced, whereas that of the latter became more soluble.
What these differences mean we are not yet in a position to say:
the chemistry of wood is complicated and not well understood.
Norman [25] states that lignin under normal conditions in plant