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 



