342 Report oF THE HorTICULTURIST OF THE 
bark, but those spores that chance to fall and germinate in a 
wound, produce the cankers. Other spores are deposited on limbs 
that have an abundance of dead and decaying outer bark where 
they find conditions suitable for growth. In such instances no 
direct injury is done to the tree, but spores are produced and dis- 
seminated so that a constant source of infection is maintained. 
The spores possess great vitality since some of them germinate 
after having been kept a year in the laboratory. 
In some instances the mycelium apparently lives over winter 
and continues its growth the following spring. The formation of 
the largest cankers can scarcely be explained in any other way. 
However, in all of the inoculations made in the spring of 1898, in 
only one instance did the resulting canker enlarge any during 
the present season. See Plate XXX, fig. 3. 
DOES THE MYCELIUM PENETRATE THE woop 2 
This question is suggested by the presence of two or more 
cankers on the same limb, the external appearance of the more 
recent ones suggesting the possibility of the fungus having passed 
from the old canker through the wood and appearing on the sur- 
face of the limb at favorable points where the newer cankers 
were formed. An examination of a number of specimens and the 
occurrence of pycnidia on decorticated wood shows that while the 
mycelium does penetrate the wood to some extent, the fact is of 
little economic importance. One limb was examined that had 
five small cankers on it at intervals of about a foot. On split- 
ting the limb it was found that the mycelium had penetrated the 
wood at but one point and that for only a short distance. 
PREVENTIVE MEASURES. 
Although experiments in treating this disease are under way uo 
results have yet been reached and from the nature of the fungus 
it will be seen that a number of years must elapse before data 
