546 BULLETIN 347 
illustrations. The effects of the disease on the general appearance of 
the tree are most noticeable during the summer, when the trees are in 
leaf. In regions where the disease is common, the newly affected limbs 
and twigs are girdled in large numbers during the summer, and the brown, 
shriveled leaves are readily seen even at a distance. This most striking 
symptom is common 
during July and 
August, while the 
healthy parts of the 
tree are still green. 
The dead leaves 
also remain clinging 
to the limbs during 
the winter (Fig. 79). 
If the girdling of a 
limb is completed 
during the time when 
the burs are matur- 
ing, the latter often 
remain on the 
branches over winter. 
If, however, the 
girdling takes place 
after leaves and 
burs are shed and 
before the leaves 
come out in the 
spring, the leaves 
do not attain their 
full size and are pale 
and distorted. This 
is a common symp- 
tom in May and 
June (Fig. 80). 
are nea - ; Dead limbs without 
- 79.— Tree during winter, showing the leaves still 
clinging to the branches, which have been killed by girdling attached leaves or 
cankers burs are often in- 
dications of the 
presence of the canker disease (Fig. 81). Water sprouts or suckers are 
commonly developed just below the cankers. Thick clumps of suckers on 
the trunk (Fig. 82), on the branches, or at the base of the tree, are 
often the only telltale evidence of a developing canker. Such growths 
