400 MANUAL OF FRUIT DISEASES 
developed. In their full maturity they appear as black specks. 
The tissue about them is vellowish. These bodies are not 
found on all leaves nor on all leaflets of a given leaf. Two or 
three weeks after the appearance of these structures evidence 
of rust is seen on the lower surface of the leaves. When mature, 
these bodies (sori) break open and expose an orange-colored 
: mass of spores; 
whence the name 
orange-rust. Ordi- 
narily these sori 
with their spore- 
masses practically 
cover the lower sur- 
face of the leaf. 
Affected leaves are 
dwarfed and rolled, 
somewhat exposing 
the orange-colored 
lower surfaces. Rust 
is rarely found on 
the canes. This 
stage gradually dis- 
appears during the 
latter part of June, 
until by July it is difficult to find in northern United States. 
Farther south, on a parallel with Maryland, orange-rust may 
be seen in late summer and sometimes in the fall. Affected 
plants are noticeably stunted (Fig. 117) but are not killed. 
Plants once affected are almost certain to be diseased again 
the following year. Some rusted plants show a reduced 
number of prickles. 
Cause. 
The bramble fungus, Gymnoconia interstitialis, is the cause 
of this disease. Its mycelium lives from year to year in the 
Fig. 117. — Orange-rust; healthy plant on right, 
diseased on left. 
