RASPBERRY DISEASES 401 
affected plant. In the roots the mycelium is. found between 
the cells of the cortex, near the cambium. As it proceeds up- 
ward the pith of the canes is invaded. In the leaves the spongy 
parenchyma is infected. In young stems the hyphe may be 
found in any of the tissues. In all these attacked organs the 
mycelium develops haustoria. These arise as side branches 
from the mycelium. They pierce the cells to get food. As an 
infected cane grows the fungus follows the growing-tip. In the 
spring on the upper surface of the opening leaves sterile black 
bodies appear. These are called spermagonia, or pycnia. Two 
or three weeks later the orange-colored cushions develop on the 
lower side of the leaf. Many spores are formed, which are 
capable of germinating at once. From each spore a short 
promycelium bearing four sporidia is protruded. These sporidia 
cause other infections on raspberries and blackberries during 
the growing-season. Mycelium develops from the sporidia. 
In the winter the fungus is again dormant as mycelium in the 
canes, crown and roots. 
Control. 
The perennial nature of this rust fungus makes it difficult 
to control. The only known remedy for diseased plants is to 
dig and destroy them. All wild blackberries and raspberries 
known to be affected should be destroyed ; they may be regarded 
as weeds in this connection. Spraying to protect healthy plants 
from infection should be beneficial, although no experimental 
data on which to base specific recommendations are available. 
The fungus has definite enemies which destroy the spores in 
large numbers. Certain insects eat quantities of spores. A 
certain fungus, Tuberculina persicina, is parasitic on the rust 
pathogene. 
REFERENCES 
Clinton, G. P. Orange rust of raspberry and blackberry. Illinois 
Agr. Exp. Sta. Bul. 29: 273-296. 1893. 
2D 
