254 SEMI-CENTENNIAL OF TORREY BOTANICAL CLUB 
progresses by the development of secondary ovoid slightly pro- 
tuberant galls, so that very often at least half of the trunk is 
girdled. The more central swellings, when they are closely asso- 
ciated, are usually dead. The whole trunk is slightly bent at 
this point. This bending is due to the inhibition of growth and 
the death and decay ‘of the region of original infection. The 
typical condition is that of death at the center and proliferation 
at the margin. In many cases the entire affected area is dead,. 
owing to the action of such agencies as fire, insects, and birds. 
Borer and woodpecker injuries in several instances were found 
to be the cause of the death of the swellings. Weir* has reported 
that borers and wood-rotting fungi, entering the burls on Pinus 
divaricata, often hasten the decline of the tree. 
While the individual swellings or galls may be circular or 
elliptical in outline, the total or final effect of the parasite on the 
host sometimes is such as to bring about a fusiform enlargement 
of the trunk. An example of .this type of infection is shown 
in PLATE 4, FIG. 2, which is from a photograph of a tree at Lake- 
hurst. The infected area is about five feet from the base of the 
tree. At the widest part of the swelling the trunk is about 
eighteen inches in diameter and tapers from this region so that 
the diameter is about four inches less at the limits of the swollen 
region. Viewed from the side this tree is seen to be bent or 
“kneed” in the manner shown іп PLATE 5, FIG. I. This figure is 
from a photograph of another infected tree from the same region. 
There are at least ten separate swellings on the canker shown in 
PLATE 4, FIG. 2. These were outlined with ink on the photograph 
so that their limits may be made out more distinctly in the repro- 
duction. If we assume that the whole canker is the result of 
one primary infection and that the point of infection is now shown 
by the presence of the oldest dead gall shown at the center of the 
picture, we see how the fungus has spread in all directions. There 
is no bark on this central gall and the exposed wood is dried and 
cracked. The second gall, just at the right, is somewhat smaller 
and circular in outline. This gall is also dead. Above the central 
gall is a large ovoid one that is dead, but not in the advanced stages 
of decay. At the right and left in this top row of swellings are 
* Weir, J. R. Observations on the pathology of the jack pine. U. S. Dept. 
Agr. Bull. 212: 1-10. 1915. 
