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 brancli forming 
the canker previously described. Within a few hours after 
