Blister Canker 
9 
where the cankers are protected from direct sunlight, but on 
the other hand light does not affect the location of cankers. 
Inoculation very often occurs thru wounds at the base of 
the tree made by rodents or by machinery in cultivation. In 
such instances, where the wounds are too large to heal over at 
once, the cankered margins advance and the bark falls away, 
but stromata are rarely found except on young trees or where 
new branches arise near enough to the wounds to be affected. 
Inoculation often occurs in roots near the surface of the 
ground thru wounds made in cultivation or otherwise. In 
such cases that portion of the root is usually killed and the dis- 
ease first becomes manifest as a canker at the crown. Some- 
times the whole root system is affected but the fungus grows 
from one root to another with much more difficulty than from 
one branch to another, so that, as a rule, even tho a part of 
the roots may be killed, the others will remain intact until 
after the whole tree has become infected. 
On the more susceptible varieties the symptoms are some- 
what different. Whole trees often appear to be killed in a 
single season and no truiting bodies appear, or one mam limb 
after another may succumb in a single season and produce 
stromata only at the base near portions of the tree which are 
still alive. In many instances stromata form on the limbs dur- 
ing the same season that the disease first appears in the form 
of visible canker, but many of them never produce spores. 
Many more never rupture the epidermis, and practically no 
ascospores are ever produced. The perfect stage of the fungus 
is rarely found abundantly on the most susceptible varieties 
except when the cankers occur on the trunk or very large 
limbs, and even then it is often wanting owing to thick, corky 
bark which hinders the formation of stromata. However, 
enough immature or sterile stromata may usually be found 
upon a minute examination of the tree to identify the disease. 
The disease makes rapid progress in trees suffering from 
drouth. The effects of drouth will be discussed later. Here 
again the symptoms are often somewhat modified. Whole 
limbs or even whole trees often die in a single season, or the 
bark may die only in long strips, sometimes reaching from the 
tip to the base of the limb, while the remaining bark will 
remain alive sometimes for several months. Infected trees 
suffering from drouth often put forth foliage and set an 
abundant crop of fruit only to have both leaves and fruit 
wither and die. In case the limb or tree does not die outright 
the leaves turn yellow and the fruit, while it reaches a certain 
