216 



MANUAL OF FRUIT DISEASES 



cultivated currants and gooseberries; this stage is known as 

 Cronartium Ribicola, the name now used to apply to any and 

 all stages of the fungus on whatever host it is found. 



The fungus lives from year to year in the bark of living pines 

 (Fig. 57), finally fruiting and developing a crop of aeciospores 

 which blow to Ribes (currant and goose- 

 berries) near by. In pines the organism 

 may be shipped thousands of miles. It is 

 not known whether the fungus hibernates 

 on the Ribes or not, although there is some 

 evidence that such is the case. In the 

 spring from early April to June (chiefly in 

 May), the aeciospores are blown to young 

 Ribes leaves. These spores are produced 

 over a period of about two weeks. They 

 apparently are never carried more than a 

 few hundred feet. Should any of these 

 spores fall on pines, infection will not re- 

 sult; the fungus cannot pass from pine to 

 pine ; it must first go to the currant or goose- 

 berry, if it is to grow. In the presence of 

 moisture the aeciospores germinate and 

 infect the Ribes leaves. Cold weather 

 inhibits the rapid progress of the fungus in 

 the currant leaves. With a favorable tem- 

 perature the fungus soon establishes itself, 

 and after two weeks a new crop of spores 

 is produced. These are always produced 

 on the lower surface of the Ribes leaf. 

 They are distinct from the aeciospores which 

 come from the white pine, and are known as uredospores. The 

 uredospores are capable of infecting other currants and goose- 

 berries. This stage is sometimes called the summer or repeat- 

 ing stage (Fig. 55). This repetition may proceed throughout 



FIG. 57. Euro- 

 pean currant-rust ; 

 secia on white pine. 



