PlftON BLISTER-RUST 
By George G. Hedgcock and Eeesworth Bethee, Pathologists , and N. Rex Hunt, 
Assistant Pathologist , Forest Pathology Investigations , Bureau of Plant Indusiry t 
United States Department of Agriculture 1 
INTRODUCTION 
A species of Cronartium on Ribes aureum has been known in Colorado 
for many years, having been collected by one of the writers (Bethel) 
in the Ute Indian Reservation in southwestern Colorado in 1897, and in 
1909 at Boulder and Denver, and various other places since that time. 3 
Since this species of Cronartium closely resembles Cronartium ribicola 
Fischer de Wald, the cause of the white-pine blister-rust, and likewise 
attacks species of Ribes, and because no species of caulicolous Perider- 
mium has hitherto been known in Colorado which could serve as its 
serial stage, it has been considered by some to be identical with C. ribicola. 
On the other hand, the occurrence of this rust at Boulder, Colo., on 
Ribes aureum for several years in close proximity to several white pines 
(Pinus strobus) which remained uninfected indicated that it was not 
C. ribicola . 
The earliest collection of this western species of Cronartium is now 
believed to be one of the uredinial stage collected by Bartholomew and 
reported by Arthur 3 (2, p. 130) in 1892 in Kansas. This was at first 
identified by Arthur (7, p. 63) as presumably Cronartium ribicola 
Arthur, upon receiving data and specimens of Mr. Bethel’s collections 
in 1909, wrote him as follows: 4 
The Cronartium on Ribes from Boulder is an interesting species. I think you are 
right in regarding it as an undescribed form, and this accounts for the uredo on Ribes 
found in Kansas, which is reported under Cronartium ribicola in the North American 
Flora (i). 
Spaulding (6) in 1911 referred to the Kansas collection as Cronartium 
ribicola , basing his action on Arthur’s first determination (7). Later, on 
seeing a specimen of the collection in Kansas by Bartholomew, Spaul¬ 
ding considered it a distinct species. Arthur and Kern (2), in 1914, 
1 The writers are under obligations to Mr. F. V. Coville, of the office of Economic and Systematic Botany, 
Bureau of Plant Industry, for the determination of species of Ribes; to*he State Historical and Natural 
History Society, Denver, Colo., for office room and other courtesies; to the officers of District 2, Forest 
Service, Denver, for cooperation in securing information regarding forest conditions; and to Mr. Hugh 
McGeary and Mrs. S. N. Keith, Bayfield, Colo., and Mr. R. Branson, Mancos, Colo., for material assist¬ 
ance in expediting the work of investigation. 
* As shown by correspondence in the files of this Office, Mr. Bethel made collections at other places in 
Colorado previous to 1909, but the material is stored and not available for examination. No localities are 
listed in this paper unless the specimens collected have been recently examined by the writers. 
* Reference is made by number (italic) to "literature cited,” pp. 423-424. 
* Letter to Mr. Bethel dated Nov. 11, 1909. 
Journal of Agricultural Research, 
Washington, D. C, v 
pb 
(4H) 
70392°—18-2 
Vol. XIV, No. xo 
Sept, 2,1918 
Key No. G-152 
