WHITE-PINE BLISTER RUST. 7 
lished in New England, New York, Wisconsin, Minnesota, and 
Canada. 
It has been known since 1892 that there was a fungus on Bibes in 
the West much resembling Cronartium ribicola, but until 1917 its 
alternate stage on pines was unknown. In that year the Office of 
Investigations in Forest Pathology began work upon this western 
fungus, which was soon found to have an alternate stage on Pinus 
edulis and P. monophylla in Colorado and Arizona (50, 114) and was 
named Cronartium occidentals. Its distribution and that of C. ribi- 
cola as known to January 1, 1920, is shown on the map (fig. 2). See 
figures 3 to 12 for the progress of C. ribicola by years from 1909 to 
Fig. 4.— Outline map of the northeastern part of the United States, showing (by black dots) the known 
(cumulative) distribution of white-pine blister rust in North America to and including 1910. 
1918, inclusive. Cronartium occidentals is found in localities where 
it could hardly be an introduction, as the Ute Indian Reservation in 
southwestern Colorado, where it was found by Bethel in 1897; also 
in the Mesa Verde region, where no cultivated Ribes or pines have 
ever been introduced. Ribes aureum is native in the Rocky Mountain 
region and is a favorite host for Cronartium occidentale as well as 
C. ribicola. 
Since Ribes aureum was intimately associated with Cronartium 
ribicola in its earlier known occurrences in Europe, an inquiry has 
been made into the possibility of the fungus being American in origin 
and its being introduced into Europe on R. aureum when that plant was 
first sent there. The facts thus far determined are 2 that R. aureum 
2 Spaulding, Perley. Ribes aureum not an original host of Cronartium ribicola. In manuscript. To 
be published in Phytopathology. 
