422 
Journal of Agricultural Research 
Vol. XIV, No. IO 
clump of Ribes sp. growing in a moderately damp place. Uredinia and 
telia are common on the petioles of the leaves and are occasionally found 
on the flower peduncles, but so far have not been observed on the stems. 
Posey, Gravatt, and Colley (5) have, in the case of Cronartium ribicola , 
found natural stem infections of Grossularia hirtella , which bore normal 
urediniospores. Melampsora bigelowii Thiim., also a common rust in 
Colorado, is known to overwinter on stems on Salix spp. here and else¬ 
where. 
During a succession of seasons favorable for the spread and over¬ 
wintering of Cronartium occidental it might be distributed in the ure- 
dinial stage to regions far distant from pinon pines. Coleosparium 
solidaginis (Schw.) Thiim. on species of Aster and Solidago, which has for 
its aecial stage Peridermium acicolum Underw. and Earle, a needle-rust of 
pines, spreads across the plains for long distances in this way. Coleo- 
sporium ribicola (C. and E.) Arth. on species of Grossulariaceae is found 
in Montana nearly 400 miles to the north of the range of Pinus edulis , 
its only known natural aecial host. The occurrence of Cronartium 
occidentale at Stockton, Kans., in 1892, as reported by Arthur (2) may 
be explained similarly. Its occurence sporadically in the parks of Denver 
and Boulder may have been the result of large plantings with stock of 
Ribes aureum shipped from Colorado points where the disease is epidemic. 
Shipments are known to have been made from Rifle, where the disease 
was especially abundant in 1917. 
In the spring of 1917 many infected leaves in a good state of preser¬ 
vation, bearing urediniosori which still had their natural color, were 
collected in the open at Denver and Bayfield, Colo., and used in inocu¬ 
lation experiments at Washington, D. C., without positive results. 
Attempts to germinate the urediniospores at the latter place failed also. 
The possibility that such urediniospores may remain viable over the 
winter should be investigated more thoroughly. 
EFFECT OF THE FUNGUS ON ITS HOSTS 
Peridermium occidentale is rarely found on very old trees of Pinus 
edulis , and in these it is in the crevices of the bark often with no ad¬ 
jacent dead areas. In such cases even when fruiting it is hardly dis¬ 
cernible with a hand lens. Its effect on young trees is more apparent. 
A number of young trees apparently killed by the fungus were found in 
southern Colorado. Such trees are usually attacked on the trunk and 
branches near the ground. Some become spike-topped (Pi. 56). Le¬ 
sions on old trees usually are found from 2 to 8 feet from the ground. 
Plants of species of Ribes and Grossularia attacked by Cronartium 
occidentale apparently suffer but slight injury, owing to the fact that 
the season's growth is made chiefly before the infection becomes heavy. 
In severe early attacks partial defoliation may result, usually late in the 
growing season. Repeated attacks may stunt somewhat the growth of 
