APPLE DISEASES 89 
are arranged radially about it. These are the fruiting pustules 
of the causal pathogene. On yellow varieties like the Yellow 
Bellflower and Tolman Sweet the spots are at first almost a 
carmine red. Later they turn brown in color. This change in 
color may occur while the apple still hangs on the tree, particu- 
larly if the weather is wet for a few weeks prior to harvesting; 
or the change may be delayed until the fruit is stored. Spots 
on affected fruit increase 
but little in size when 
placed in cold storage. 
Cause. 
The fungus Phoma pomi 
produces this apple fruit- 
spot disease. The patho- 
gene probably hibernates 
in the form of sclerotial 
masses and as_ peculiar 
thick-walled cells known 
as chlamydospores. 
These structures winter 
over on fallen fruit. 
With the advent of the 
growing season conidia originate from both the sclerotia 
and the pycnidia on the fallen fruit, and these spores bring 
about the first infections of the year. Observations show 
that a larger number of the inoculations take place in July or 
early August. None occur after the last of August. Entrance 
into the fruit is gained by way of the stomata. After the 
spores are deposited on the apple fruit fifty days may elapse 
before there are any signs of the disease visible to the unaided 
eye. Owing to this condition of affairs fruits may be inocu- 
lated before picking but show no evidence of fruit-spot at the 
time of harvest. In due time, however, the disease develops 
in storage or in market. On entering the apple-tissue the germ- 
Fic. 24. — Apple fruit-spot. 
