420 
Journal of Agricultural Research 
Vol. XXV, No. 10 
became infected until late in the summer, although many inoculations 
were attempted. On plants of these two species the infected areas 
developed slowly until they became from 2 to 4 mm. in diameter. The 
invaded tissues often die soon after infection. Uredinia are scanty if 
produced at all, and few spores develop. The incubation period for 
these two species may be as long as 36 days, although 15 days are the 
maximum for other species. The disease has not been observed to 
spread to new areas or to new leaves on plants of these species. 
The leaves of many plants were carefully examined with a hand lens 
almost daily, beginning 5 or 6 days after the date of inoculation. In no 
case were uredinia found forming in less than 10 days following inocula¬ 
tions with aeciospores, nor in less than 9 days following inoculations with 
urediniospores. Urediniospores are normally produced in 12 to 15 days 
after inoculations with either form of spores, except as noted above for 
R. americanum and R. nigrum . 
A summary of inoculations with urediniospores during 1917 and the 
spring of 1918 at Washington, D. C., is given in Table I. Urediniospores 
and teliospores were produced throughout the winter, successive inocula¬ 
tions being made every six weeks. 
INOCULATIONS WITH TELIOSPORES 
The first inoculations with the telia of Cronartium occidentale from 
Ribes aureum sent in from Colorado were made in 1914. Others were 
made in 1916. The material used in these inoculations was in such 
condition that probably no viable teliospores were present, as no results 
have been obtained. In 1917 about 4,000 inoculations were made on 23 
species of pine. The larger part of these were made in the field, in 
Colorado and Arizona, but a considerable number were made in the 
greenhouse at Washington, D. C. It is hoped that some indication of 
the results may be obtained during 1918 either through the development 
of pycnia or by determining the presence of the mycelium of the species 
of Cronartium by Colley's method (j). 
DISSEMINATION OF CRONARTIUM OCCIDENTALE 
Cronartium occidentale , like other species of the genus Cronartium in the 
United States (4, 6 ), is disseminated in three spore forms: iEciospores, 
urediniospores, and teliospores. 
Although the aecia of the Peridermium form of this fungus on Pinus 
edulis were first found in the fruiting stage on May 25, they may some¬ 
times mature at a somewhat earlier date. Viable spores of the Perider¬ 
mium were found in specimens collected in southern Colorado as late as 
September 21. The aeciospores are discharged slowly, owing to the fact 
that they are held under the bark in large flattened cavities which 
rupture by means of narrow rifts in the bark. In 1917 the aeciospores 
were not found infecting Ribes spp. at a greater distance than a hundred 
