18 MANUAL OF FRUIT DISEASES 



oval in shape, measuring one or more inches in length. With 

 increase in size the edges become more or less ragged and the 

 surface is somewhat roughened. The dead bark is cracked and 

 fissured. In some instances it is broken away, although it 

 ordinarily dries out and adheres to the wood. The major 

 portion of the canker is at last clearly depressed, while about 

 the margin of the dead area is formed a callus. 



Bitter-rot is not known to occur on the leaves. 



Cause of bitter-rot. 



The pathogene causing this disease is Glomerella cingulata. 

 The fact that the same organism is responsible for both the 

 rot and canker forms of the disease has been fully established. 

 For example, the fungus may readily pass from the bark to the 

 fruit, and this fact is highly important in its life-cycle. Fol- 

 lowing the seasonal development of the pathogene, it is to be 

 noted that there are two chief sources of the inoculum in the 

 spring ; these are the mummies which hang to the tree through 

 the winter, and the cankered areas in the limbs. From these 

 sources conidia are washed by rains to the susceptible parts 

 below, that is, young fruits and limbs. Insects appear to have 

 little to do with the dissemination of the fungus. The best 

 evidence that a canker or a mummy are sources of the inoc- 

 ulum, and that rain is the inoculating agent, is found in the 

 fact that affected fruits usually map a pyramidal area at the 

 apex of which is found a canker or a mummy. Furthermore, 

 infections on fruits are frequently arranged in lines toward the 

 calyx-end, which indicates that the spores were washed by 

 water down the sides of the apple. The conidia soon germinate, 

 their germtubes being capable of entering through the healthy 

 surface as well as through wounds. Abrasions in the bark of 

 various sorts furnish a channel of entrance into larger limbs. 

 The fungus may be able to penetrate uninjured twigs and from 

 these organs it spreads readily into the parent branch forming 

 the canker previously described. Within a few hours after 



