Blister Canker 
17 
greenhouse before that. Over 2,000 field inoculations were 
made in trees of several varieties, ranging from 1 to 16 years 
old. Inoculations were made in every manner in which it was 
thought possible that infections could occur under field condi- 
tions. Ascospores, conidia, infected wood tissues, and pure 
cultures of the fungus were used as inocula. 
In making the inoculations with pure culture and infected 
wood the surface to be inoculated was first washed with 95 
per cent alcohol. The wound was then made with a sterilized 
knife, chisel or auger as the case might be. The inoculum was 
placed in position and the wound covered with a sterile cotton 
patch. This was in turn covered with a square of cloth coated 
with paraffin and the whole then wrapped with several layers 
of cloth saturated with grafting wax. The inoculations with 
other inocula were covered in the same way but the surface to 
be inoculated and the tools were not sterilized except in a por- 
tion of the operations. Care was exercised to use trees free 
from previous infection. To determine whether or not a tree 
was infected one or more large branches were sawed off close 
to the trunk, or borings were made with an auger, and trees 
which showed discolored wood were rejected. 
ASCOSPORE INOCULATIONS 
The spores were secured by cutting away the disc from a 
stroma and exposing the perithecia, then drawing out the 
spores by means of a pipette partly filled with water, or by 
causing the spores to be expelled and collecting them from the 
petri dish covers as has already been explained. The spores 
were placed in water in a bottle and inserted in the incisions 
by means of a bulb pipette. 
Inoculations were made by spraying spores upon the unin- 
jured surface of the bark of limbs and current growth,* and 
in like places after the bark had been bruised but not broken 
open. Others were made where the surface had been cut away 
but the cambium left uninjured. Inoculations were also made 
on current growth in the region of the cambium, by lifting the 
bark with a knife and inserting the spores, and in the xylem 
by making a slanting cut or by removing a portion of the 
wood. ^ The same method of procedure was followed in making 
inoculations on older limbs except that a greater amount of 
wood was removed. The cuts were made to extend thru a 
definite number of annual rings from one to five below the 
*By current growth is meant growth which occurred during the season 
in which the inoculations were made. Wood which matured the previous 
year is called one-year-old wood. 
