APPLE DISEASES 85 
favorable to spore-germination. The fungus is capable of 
entering its host through wounds in the bark and fruit; how- 
ever, these wounds are not necessary to penetration. The 
uninjured bark is penetrated in most cases, chiefly through the 
lenticels. The healthy, uninjured skins of fruits may be pene- 
trated directly. The fungus in the fruits produces the rot 
already described, but such fruits apparently never play any 
further part in assisting the fungus to complete its life-cycle. 
The fungus undoubtedly perishes with the destruction of the 
affected fruit. In the limbs, however, the fungus develops 
advantageously. It grows slowly after entrance into the bark, 
killing the bark-cells as it progresses. The cambium, sapwood, 
and even the heart-wood are also affected beneath the canker, 
but there is no evidence that new cankers arise by growth of 
the mycelium to points above or below such lesions. As pre- 
viously pointed out, the fungus develops very slowly during 
the winter. The following March and April growth is resumed ; 
growth ceases, however, with the initial spring activities of the 
cambium. By midsummer, the acervuli are produced, and the 
first year’s cycle is completed. 
In the fall, two years after infection, the sexual stage of the 
fungus develops in the old cankers (Fig. 23, center). The 
fruiting bodies formed are apothecia. They arise in the clefts 
in the bark formed by the old acervuli, developing in the mycelial 
cushions left by these asexual structures. Under the moist con- 
ditions of the autumn the apothecia become swollen; if dry 
weather prevails for a time, they seem to disappear, and then 
to reappear with the return of the next wet weather. If 
favorable conditions prevail for any length of time, the asci 
elongate, swell, and the ascospores are finally ejected forcibly. 
These spores are carried by the wind to the susceptible organs 
of the apple, where infection results as described for the conidia. 
It is to be noted that the conidia may continue to develop 
in a canker for at least three years. Thus cankers from one 
