Blister Canker 
33 
the trunk. When the cankered area reached the trunk there 
was no further external evidence of growth until the mycelium 
had invaded the outer rings of wood in the trunk when the 
cankered area was again enlarged. 
INOCULATIONS IN TREES OF DIFFERENT AGES 
A number of inoculations were made in young trees of dif- 
ferent ages to ascertain if susceptibility to attack by blister 
canker was in any way associated with the age of the trees. 
Trees of several varieties ranging from one to four years of 
age at the time of inoculation were used. The data in table 7 
indicate that, as in the case of inoculations in limbs of mature 
trees, the age of the wood inoculated is a more important fac- 
tor than the age of the tree. 
ROOT INOCULATIONS 
Inoculations with ascospores were made in the roots of 
Ben Davis and Jonathan trees. The roots were uncovered, 
and inoculated in the manner already described. Wires were 
attached which would reach above the surface of the ground 
and zinc labels attached. The soil was then replaced. The 
data in table 8 show the results of these inoculations. 
The mycelium travels much slower thru the roots than 
thru the upper portion of the tree. That this is not alto- 
gether due to the cellular structure is shown by the fact that 
in a number of the roots examined the tracheae are much more 
numerous and are larger than in the trunk and limbs. How- 
ever, pits in the cell walls of the roots examined were not so 
numerous as in the cell walls of tissues in the branches. That 
cellular structure does modify the rate of growth to some ex- 
tent is shown by the fact that the mycelium passes very slowly 
and with difficulty thru the region of the crown of the tree 
where the cells are greatly distorted and compressed. It was 
noted that this was true whether the infection came from the 
branches or the roots. No doubt the growth in the roots 
is retarded to some extent on account of lack of oxygen. That 
this must be true is shown by the slower growth of mycelium 
made in roots situated rather deep in the soil, while in those 
at or near the surface the growth was found to be almost as 
rapid as in the trunk and branches. Growth may also be re- 
tarded by the abundance of sap in the roots. The severing of 
a root at or just beyond the inoculation caused the growth of 
mycelium to be much more rapid, and as will be shown later 
the checking of absorption of water by increasing the osmotic 
