APPLE DISEASES 63 
Rust 
Caused by Gymnosporangium Juniperi-virginiane Schw. 
This disease is variously known as cedar-rust, cedar-rust of 
apple, cedar-apple, apple-rust and cedar-flowers. It affects 
not only the apple and wild crab, but also the red cedar. Both 
kinds of plants are necessary in the same immediate locality 
for the perpetuation of the rust-pathogene. If the cedar is 
absent, there can be no apple-rust. 
With respect to the apple, a great many lists of susceptible 
and resistant varieties have been published from various 
parts of the country. These lists agree in part, but it is of 
interest to note that certain varieties are classed as susceptible 
in one state and as resistant in another. The Ben Davis, for 
example, is said to be resistant in Delaware, Massachusetts, 
Rhode Island and Nebraska, but is reported as being susceptible 
in Iowa and Virginia. The Rome is susceptible in Alabama, 
Indiana, West Virginia and other states, but is resistant in 
Delaware. Similar examples of such variation are found in 
the Grimes and Red June. While there may be some variation 
due to the difference in location, it appears that the judgment of 
the individual as to what constitutes resistance or susceptibility 
is a more probable explanation. Different periods of rust- 
infection may give rise to confusing data, since the leaves of 
one variety may expand more quickly or may have a shorter 
or longer period of susceptibility than the leaves of another 
variety. It has been found that varieties are susceptible only 
while the leaves are young; after maturity, they are im- 
mune. It has been learned also that the morphological make- 
up of the leaf, as, for example, hairiness, has nothing to do with 
the question of its susceptibility. 
In spite of these uncertainties with respect to varietal resist- 
ance, it is generally agreed that the York Imperial is very 
susceptible. Others in this class are the Rome, Wealthy, 
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