Enporuia CANKER OF CHESTNUT 549 
ruptured apices of these blisters (Plate XXXVIII, Fig. 1). Older and 
larger cankers have the 
pimples and the yellow 
tendrils confined to the 
margin, while nearer the 
center reddish-brown 
pustules have been pushed 
out through the outer 
bark. These pustules, 
when fully developed, 
measure one sixteenth of 
an inch or more in 
diameter and have 
numerous papilla on the 
upper surface, each with 
a black dot at the tip 
(Plate XX XVIII, Fig. 2). 
Cankers on rapidly 
growing limbs are usually 
outlined by a distinct 
ridge of slightly hyper- 
trophied tissue. Where 
the whole cankered area 
is hypertrophied the bark 
usually splits longitu- 
dinally (Plate XX XVII). 
As the canker becomes 
older the bark splits and 
cracks, and after a few 
years it breaks away 
entirely and leaves the 
wood bare (Fig. 83). 
When the tree is 
thoroughly diseased — and 
this may take only two 
or three years after the 
first infections occur if 
they are at the top of the 
tree —the brown pustules 
cover the bark of the 
trunk and the branches, 
giving the tree the distinc- 
Fic. 82.—Water sprouts on the trunks, indicating cankers 
just above them 
