270 FIFTEENTH ANNUAL REPORT OF THE 



blisters or bags blows a dark yellow powder, consisting of the reproductive 

 cells, or so-called spores, of the fungus, which are carried great distances 

 by the wind. These spores can not develop unless they fall on the leaves 

 of currant or gooseberry bushes, in other words on plants belonging to the 

 genus Ribes. On these leaves they germinate, however, especially on Ribes 

 nigrum, aureum, and sanguineum, but also on other species. The germ tubes 

 enter the leaf tissue and felt into a mat of countless threads (Mycelium). 

 After a few weeks, about the beginning of June, these form on the underside 

 of the leaves of currant and gooseberry bushes bright yellow deposits of new 

 reproductive cells, called Uredospores, which spread the disease from leaf 

 to leaf of the Ribes bushes. On all the leaves on which these cells happen 

 to fall, similar yellow deposits are formed in a short time. This increase 

 and distribution lasts the entire season, so long as the young leaves are formed. 

 In the summer, however, still other reproductive cells (Teleutospores) are 

 deposited on the underside of the infected leaves, which appear in the shape 

 of yellow brown strings or sausages of the thickness of a hair. On the sur- 

 face of these strings, tiny cells are deposited, so-called sporidia, which germ- 

 inate only on the bark of young shoots of the white pine, but not on currant 

 or gooseberry bushes. 



' The relation between the white pine blister and the Ribes fungus 

 which bears the name of Cronartium ribicolum, has been established by 

 artificial infection, so that it is certain that the first (Peridermium strobi) 

 is but a stage in the development of the second {Cronartium ribicolum). 



' The last named sporidia, which come from the Ribes fungus, are 

 produced and carried by the wind at the very season that the young white 

 pine shoots have begun to develop and are in a condition to be readily 

 infected. When the small sporidia germinate their germ tubes penetrate 

 the tender bark of the white pine and there mate again (Mycelium) . This 

 tissue lives for many years in the branches and occasions considerable 

 swelling of the shoots, by which the disease may be detected, also in the fall 

 and in the winter when there are no yellow deposits on the bark. 



" On the surface of the infected branches, probably not until several 

 years after the infection, spore blisters are formed, such as are described at 

 the beginning of the article. For a number of years these reappear every 

 spring on the same swelling. (Their appearance is preceded by the forma- 



