DopGE AND ADAMS: PERIDERMIUM CEREBRUM 255 
two living galls, the smaller of which is producing aecidiospores. 
The larger one at the left was covered with a thick mass of pitch 
at this time. On the lower parts of the infected region are five 
or six other galls, the larger one being dead while the others are 
alive. 
'The question as to the manner in which the fungus comes to 
attack new regions is an interesting one in view of the fact that 
we have these separate galls, all evidently resulting from one 
primary infection. The spread of Ше mycelium appears not | 
to be by gradual encroachment but rather by sudden migration 
induced by the conditions that are to bring about or have already 
brought on the death of the tissues of the gall. Some light may 
be thrown on this question by a study of the specimen figured in 
PLATE 5, FIG. I, which is a side view of a portion of a tree ten inches 
in diameter at the cankered region. The marginal gall (at the 
right in the picture) is alive, but the other two, both furrowed and 
denuded, are in advanced stages of decay. A cross section of 
this same specimen is shown in PLATE 6. The tree was plainly 
infected when it was very young, evidently in the growing region 
of the stem at a point about two feet from the ground. The 
wedge-shaped abnormal discolored gall-tissue can be traced to 
within three or four rings of the center. By splitting the central 
wedge we find that, further down, the infected area approaches 
the very center of the tree. The first gall growth has entirely dis- 
appeared, owing todecay. The fungus hasspread peripherally by 
a series of sudden localized migrations. At the right (above) the 
first migration occurred about the tenth year, and about the four- 
teenth year at the right-center (below). Both migrations resulted 
in the formation of large, lobed or furrowed galls, the wood of 
which is now discolored and decayed. Just when the other 
migrations took place is difficult to determine. At the upper left 
corner a distortion of the annual ring is evident at about the 
twenty-sixth year. At the lower left, the wedge-shaped band 
of solid, dark-colored wood begins with the eighteenth year and 
spreads out gradually for eight years more before this section 
shows the beginning of the globoid gall. It has evidently taken 
nine years for the upper swelling at the left to develop, although 
the larger amount of the characteristic gall tissue has been formed 
during the last three years. 
