256 SEMI-CENTENNIAL OF TORREY BOTANICAL CLUB 
Infections sometimes occur at the base of a tree, as shown in 
PLATE 5, FIG. 2. This infection has spread peripherally very 
rapidly. The dark area, at the right of the center, is dead, but 
the bark still adheres. The other lobes of the gall are producing 
aecidiospores. 
The prevailing type of trunk infection on P. rigida in the pine 
barrens of New Jersey is interesting when compared with those 
observed by Weir (1. c.) on P. divaricata. He points out that 
Peridermium Cerebrum in dry sandy areas confines itself more 
generally to the branches, occurring more rarely on the trunk. In 
the pine barrens the older swellings are very rough in appearance. 
Several layers of loose scaly bark are usually found adhering. 
This is the tissue that is sloughed off after the development of 
spermogonia or aecidia. It adheres most strongly at the margin 
of the infected areas. The outer younger swellings possess а 
smooth tan-colored layer of cork tissue. 
In cross sections of the trunk the dark wood of infected areas 
contrasts so markedly with the healthy wood that the time at 
which infection took place can be determined fairly accurately. 
In eight trees that were cut where the disease was restricted to 
the trunk, it was found that infection had occurred when the 
trees were from one to four years of age. Cross sections of 
typical globoid galls on P. virginiana from Bedford, Virginia, 
show that infection usually takes place during the first year’s 
growth. Stewart (7. c.) has stated that infection on P. Banksiana 
usually, if not always, occurs during the first year's growth of the 
branch. Where it is possible to trace the annual rings of growth 
in P. rigida through the infected and uninfected regions, it is 
found that about twice as much wood is formed in the diseased 
region as in the healthy. 
The mycelium is uninucleated and its intercellular develop- 
ment is abundant in the cortex. The hyphae appear to follow 
the medullary rays in the cortex as well as in the wood where the 
mycelium is more sparingly developed. 
Haustoria are commonly developed in the cells of the medullary 
rays. They are not exceptionally large and have the usual con- 
striction where the cell wall is penetrated. They are of about the 
same diameter as the hyphae from which they originate and are 
