204. TRANSACTIONS OF THE ROYAL CANADIAN INSTITUTE [VOL. XII 
Microscopic examination of the decayed wood shows that cellulose 
is removed from the walls of the structural elements, leaving the middle 
lamellae intact and the secondary layers represented by a gummy sub- 
stance which cracks in the manner shown in Figures 13 and 14. In 
Figure 14 the tracheids at the extreme right have not yet been attacked 
and the bars of Sanio are obvious. The two lines of the X-shaped cracks 
where the wall has been perforated or on the bordered pits may be on 
opposite sides of the wall. With the removal of the cellulose there is 
apparently a shrinkage in volume which affects the entire mass of 
affected wood and which is responsible for the fracturing. The cracks 
in the walls of the tracheids are similar to those produced by Polyporus 
Schweinitzii and P. sulphureus as described by Hartig!°—an effect that 
may be common in all cases where there is a removal of the cellulose 
only. 
TEXT-FIGURE 1. 
A transverse section of Pinus Strobus decayed by F. officinalis, showing a breaking down of the tissues 
around the resin canals. 
As to the importance of Fomes officinalis as a destroyer of dead 
coniferous timber there can be no question. While preferring the heart- 
wood, it works outward so that but a thin shell of sound wood remains, 
and if there be a sufficiency of moisture, the entire sapwood, as well as 
the heartwood, is involved. It likewise works vertically through the 
trunk, destroying in a tree most of the wood of merchantable value. 
Fallen timber and standing trunks are destroyed alike. Weakened 
by the decay, the trunks of standing trees often snap, the break taking 
