CURRANT DISEASES 217 
the growing-season, a new generation of uredospores being pro- 
duced every two weeks if conditions favor. Thus the fungus 
spreads rapidly and over great distances, assuming, of course, 
that Ribes are present. 
From the latter part of July until leaf-fall, spores of another 
kind are formed on the currant and gooseberry leaves (Fig. 
56). They are recognized as groups of three to twelve stout 
threads, measuring a quarter of an inch or less in length. The 
spores of this stage are called teliospores. The teliospores 
differ from the uredospores in that they cannot reinfect the 
currant and gooseberry. They germinate in a peculiar fashion : 
a short tube is produced on which small spores, called sporidia, 
are developed. The sporidia are extremely light and are blown 
easily by the wind. These blow to the white pines, germinate, 
and infect the bark of the same. The mycelium resulting 
spreads through the bark for several inches, but there may be 
no external evidence of the disease for several years (one to 
six or more). ‘Finally the bark begins to thicken, and the first 
external evidence of the fungus itself consists of minute ‘bodies 
known as pycnia; these appear from June to September. 
Closely following the development of the pyenia are the ecia. 
Spores from the ecia blow back to the currants and goose- 
berries. 
Control. 
From the point of view of the people at large the removal of 
the less important host would involve the currant and goose- » 
berry. But in some cases the commercial grower of bush-fruit 
should destroy the white pine only in those cases where but a 
very few trees stand in close proximity to the berry plantation. 
The safety-zone may be put at five hundred feet; that is, the 
two hosts, white pine on the one hand, and currants and goose- 
berries on the other, should not be allowed to grow within a 
distance of less than five hundred feet of each other. It is safer 
at present to destroy those Ribes plants which are persistently 
