February, ’18] 
PRIMM: EUROPEAN POPLAR CANKER 
131 
responsible in each case. The indications are that the fungous has 
been present much longer than these first reports would indicate. 
Whether the cankers produced on Lombardy poplars thirty years 
ago, as stated by two nurserymen of this state, were produced by 
Dothichiza, is very doubtful. Other canker-producing fungi are quite 
common on both poplars and willows, while Schizoneura transversitatis 
sometimes induces a condition almost identical with a healed over 
canker. 
The typical injury from the poplar canker results directly from the 
death of the cambium in the infected area. Unless a canker com¬ 
pletely encircles the trunk, the tree may live for several years and 
even when badly attacked by a number of cankers, there is often 
sufficient vigor left for new growth to be produced and for maintaining 
a scarred and unsightly existence. Each year the dead branches 
become more numerous and conspicuous, the beautiful spire-shaped 
outline of the tree is destroyed, unsightly water sprouts form below 
the cankered areas, the dry leaves hang on late in the fall and the 
trunk is likely to be snapped in two by slight wind storms. Again 
the whole top of the tree may be killed immediately by an encircling 
canker and oftentimes the whole tree. If the outer bark is stripped 
from a badly diseased tree, the irregular brown colored areas where 
the cambium has been killed are readily seen. Cankers often form 
at the base of the lateral branches and one after another the branches 
become infected and die. 0 
The cankers first appear as depressed and slightly darker areas of 
bark, their greatest dimension usually parallel with the axis of the 
trunk or branch. They are usually tapering at the ends and may 
occur anywhere on trunk or limb but in most cases about the base of 
branches or twigs or where conspicuous wounds have been made. 
As the canker becomes older it may cover quite an extensive and 
irregular area. One canker mentioned by Hedgcock and Hunt, was 
twelve inches long and encircled the trunk of the tree for nearly two- 
thirds the length of the canker. Incipient cankers have been found 
by the writer in the wounds made by the egg punctures of the Buffalo 
tree-hopper. It is also significant that in a block of balsam poplars 
which were seriously infested by the poplar weevil (Cryptorhynchus 
lapathi), every tree so infested was also badly cankered, while some 
Lombardy poplars in a block adjacent and not attacked by the weevil 
were correspondingly free from the canker. 
Soon after the development of the sunken areas, in April and May, 
numerous pustules or blisters push up from beneath the bark. These 
rupture in a short time and a sticky, amber-colored mass of spores 
exude, which dry up a month later and assume a darker walnut brown 
