346 MANUAL OF FRUIT DISEASES 
Fig. 96. — Pacific Coast rust on pear-fruit. 
times witches’- 
brooms are formed ; 
these may attain 
a diameter of two 
feet. 
Cause. 
The Pacific Coast 
rust fungus may 
properly be called 
Gymnosporangium 
Libocedri. Sporidia 
developed from teliospores on the incense cedar are blown 
for a considerable distance to the pear and other pomaceous 
fruits, where they cause infection. Within a few days after 
the pear is inocu- 
lated by sporidia, 
spots become visi- 
ble on the affected 
organ as a result 
of infection. 
Within a month 
or less after inocu- 
lation mature ecia 
are present. 
From the ecia 
great numbers of 
zeciospores are pro- 
duced. These are 
liberated and are 
carried by the 
wind to the incense 
cedars, where in- 
fection results. 
The mycelium of 
Fic. 97.— Pacific Coast rust of pear; telial stage on 
incense cedar. 
