Sept. 2,1918 
Pinon Blister-Rust 
4 i 7 
District or Columbia, Washington; 1 
On Ribes americanum. — Hunt, November 11: 
On Bibes aureum. — Hedgcock, August 31, September 8, 19, and 21, and Hunt, 
November 3. 
On Ribes giraldi. — Hedgcock, September 21, and Hunt, November 3. 
On Ribes malvaceum. — Hedgcock, September n, and Hunt, November 3. 
On Ribes nigrum. — Hunt, November 3. 
On Ribes sp.—(near R. aureum) Hedgcock, September 21. 
Kansas: 
On Ribes aureum . —Rooks County, E. Bartholomew, August 22, 1892. (First 
collection of uredinial stage.) 
•Although the survey for Peridermium occidentale was continued in 
Colorado throughout the summer of 1917 until late in October, only 42 
trees of Pinus edulis were found diseased by it. These were found in 
five widely separated localities. In Arizona only one diseased tree of 
Pinus monophylla was found late in the season. The finding of telia 
on Ribes aureum in Arizona in the vicinity of trees of Pinus cembroides 
indicates that this also may be an, secial host. No survey was made of 
regions where Pinus quadrifolia is found. These four species of pine 
are known as pifion pines. Since this rust is the only one known to occur 
on the stems of pifions, and is, so far as known, confined to pifions, it is 
called the “pinon blister-rust/' 
Peridermium occidentale has not been found on the native white pines 
Pinus aristata and P. flexilis , although both species occur frequently in 
association with Grossularia leptantha and Ribes inebrians , which are 
native hosts for the Cronartium. These species of Grossulariaceae often 
range from the pifion belt, where P. edulis abounds, to the higher alti¬ 
tudes, where the white pines occur, furnishing a means for spreading 
the rust in the uredinial and telial stage from the former species of pine 
to the latter if they were susceptible. 
Cronartium occidentale in the uredinial and telial stages was collected 
in 1917 in 18 localities in Colorado and 5 in Arizona. Although all of 
these"collections except those at Denver and Boulder, Colo., were made 
in regions where pifion pines occur, the Peridermium stage was collected 
only in 6 localities. Ribes aureum is the principal host for the uredinial 
and telial stages in nature and is usually heavily infected under favorable 
conditions, especially along streams and under moist conditions. At 
Glenwood Springs, Colo., Grossularia leptantha , growing on dry hillsides 
was abundantly infected, while R . aureum and R. inebrians were found 
infected in only one locality for each, and of the latter species only one 
clump or bush was infected. R. odoraium has been planted in many 
gardens in and around Prescott, Ariz. This species is doubtfully dis¬ 
tinct from R. aureum , is equally susceptible* to the fungus, and was 
abundantly infected at Prescott. Cultivated currants (Ribes spp*) and 
1 All collections from the District of Columbia are from artificial inoculations made in the greenhouse at 
Washington by Messrs. Hedgcock, Hunt, and Rhoads. 
