1914) 
VON SCHRENK—A TRUNK DISEASE OF LILAC 257 
percentages of either may make the conditions unfavorable for 
further development. 
In the Шас disease the fungus may grow outward concentrically 
in а regular manner (pl. 9 fig. 1). Very frequently, however, 
the fungus grows out into the sap ring at one side, at first slowly, 
then more rapidly. This is well shown in pl. 9 fig. 2, where 
four successive stages are represented by photographs. In 
the upper left-hand trunk the fungus has almost reached the 
bark, and in the three lower ones it has reached the bark and is 
gradually killing it. "The probable explanation for this behavior 
is to be sought in the water content of the wood fibers. It was 
found that in many cases where the fungus actually grew up to 
the bark and through it, that on that side the lilae borer had 
been active; the wood fibers in the vicinity of the holes dried 
sufficiently to make growth possible for the mycelium, and as 
the destruction took place more drying occurred in adjacent 
areas until ultimately the whole sap region on that side was 
invaded and destroyed. 
A number of water determinations were made of the wood 
fiber in the immediate vicinity of the growing mycelium, and 
the results compared with those obtained from normal sap-wood. 
In all eases the sap-wood about to be invaded was found to 
have a very much lower water content than the normal sap- 
wood. Unfortunately, it was impossible to get exact data which 
would indicate accurately the highest moisture content at which 
growth was possible; infected wood had obviously already 
reached and gone beyond that point, and as to sound new wood, 
even that which was near the borer holes, nothing could be 
postulated with certainty concerning its susceptibility or non- 
susceptibility to fungous attack. It would be an interesting 
problem to test the water susceptibility of Polyporus versicolor 
in its relation to lilae wood. It seems probable, however, that 
the drying out of one side of the trunks was at least one of the 
determining factors in the rather striking and exceptional 
method of growth of the fungus. Whether the fungus would 
eventually have destroyed the entire trunk it is impossible to 
state, because no such wholly destroyed trunks were found, 
There seems to be no reason, however, why this should not 
