418 
Journal of Agricultural Research 
Vol. XIV, No. 10 
gooseberries were frequently found in Colorado in regions near badly 
diseased plants of R . aureum, but were never found infected. At Pres¬ 
cott a few plants of cultivated gooseberries (Grossularia reclinata X G. 
hirtella) were found to be slightly infected. 
The apparent rarity of Peridermium occidentals is perhaps due chiefly 
to the fact that plants of susceptible Ribes are not of common occur¬ 
rence in pinon forests. In localities at 8,000 feet or more in elevation, 
as in the San Luis Valley in southern Colorado, Grossularia leptantha is 
common among pifions, but lower down on the pinon mesas no species 
of Ribes are found except along the streams. Here R. aureum occurs 
frequently. In such localities agricultural activities have removed most 
of the trees of Pinus edulis , which formerly grew there in abundance. 
The pinons of Colorado are all of the 2-leaved species, Pinus edulis , 
and are found almost exclusively west of the 106th Meridian and south 
of the 39th Parallel (fig. 1). They occur at an altitude of 5,000 feet to 
8,500 feet, although in exceptional cases, as on Marshall Pass, they ascend 
to nearly 10,000 feet. They cover an area of more than 40,000 square 
miles of the State, chiefly the mesas (low table-lands) in isolated areas. 
Only a small part of this region was surveyed during 1917, owing to the 
lack of time and because of the difficulty of access, since there are few 
railroads or automobile roads in this section. 
INOCULATIONS WITH CRONARTIUM OCCIDENTALE 
INOCULATIONS WITH ^CIOSPORES 
The first inoculations with the aeciospores of Peridermium occidentals 
from Pinus edulis were made at the pathological greenhouses at Wash¬ 
ington, D. C., on June 1, 1917, with material (FP 24667) collected on 
May 25. Plants of Castilleja linearifolia , Gomandra umbellata, and 
Ribes odoratum were used. On June 14 one of the plants of R. odoratum 
was found to be infected with a species of Cronartium. Two more 
R. odoratum plants were immediately inoculated with spores from the 
same lot of serial material. On June 25 abundant uredinia were observed 
to be forming on several leaves of both plants. Successful inoculations 
were also made under rigid quarantine conditions in a unit of the quar¬ 
antine house of the Federal Horticultural Board. Other aeciospore 
inoculations were made at various times with material from different 
collections and localities. Inoculated plants of R. aureum , R. odoratum , 
and of Grossularia inermis , and one plant of R. americanum became 
infected, but those of R . nigrum and G. missouriensis remained unin¬ 
fected. Control plants of all species were uninfected. The last success¬ 
ful aeciospore inoculation-was made on October 2, 1917, with material 
collected on September 21. No infections resulted where the aeciospores 
used had been collected and kept for more than 20 days. Table I gives 
a summary of the results of the inoculations with aeciospores and uredi- 
niospores at Washington, D. C. 
