30 ANDERSON: DASYSCYPHA RESINARIA CAUSING 
trunk a glazed appearance easily seen at some distance from the 
tree. The exudation of resin from the canker spot, however, is 
not due entirely to the early drying and forcing of the resin out 
of the vesicles, but also to an increased resin secretion at the 
cambium and parenchyma cells of the secondary cortex. The 
resin-canals and vesicles for the storage and reception of the re- 
sin having, as explained, already been cut off, a part of this resin 
diffuses into the outer dry bark but the remainder is forced to the 
surface where it collects in drops (Fig. 3, ¢) which hardens as soon 
as exuded, or when the exudation is profuse a part of the resin 
flows down the trunk. 
THE SECONDARY CORTEX (INNER Bark) 
The cambium at the canker spot produces an increased num- 
ber of cortical as well as wood-cells. The secondary cortex does 
not depart much from the normal in its structures, except in its 
increased thickness, often eight to ten times that of the normal, due 
to the greatly increased number of cells formed. The secondary 
cortex is normal in that it does not contain any resin-canals nor 
resin-vesicles, 
THE Woop 
The annual rings of the wood formed at the canker are wider 
than those formed before the infection. This increased width of 
the rings is due to an increase in the number of tracheids produced 
by the cambium. These tracheids, as well as the cells of the 
medullary rays, are usually of a greater diameter than the normal, 
which also accounts for the greater width of the rings formed at 
the canker. 
This increased growth of wood and cortex takes place any- 
where the cambium still remains alive. In all of the cankers ex- 
amined, the cambium had been killed, usually about the center. 
The dead spot varies in size in different cankers but it seldom ex- 
tends completely around the stem or branch. When it does, as in 
fig. 1, the branch becomes girdled at this place and soon dies. 
More often the dead area is small, remaining about the same size 
for a period of years. An effort is made by the living cambium 
surrounding the dead area to heal it over. This it is not able to 
do on account of the fungus mycelium. With the increase in the 
Basement 
