12 BULLETIN 247, U. S. DEPARTMENT OF AGRICULTURE. 
DISSEMINATION OF THE FUNGUS. 
Cronartium pyriforme is disseminated by means of its three spore 
forms — viz., seciospores, urediniospores, and teliospores — each form 
playing an important role in maintaining the succession of generations 
between pine trees and Comandra plants. The process of infection 
with this species of rust does not differ materially from that of the 
white-pine blister rust (12). 
The secia on the table mountain pine (Pinus pungens) in Pennsyl- 
vania mature from the middle of May to the latter part of June. 
Farther north on the jack pine (Pinus divaricate) they bear their 
spores somewhat later in the season. On the lodgepole pine (Pinus 
contorta) and the western yellow pine (Pinus ponderosa) from Colorado 
to Wyoming, the period of maturity is from the middle of June to the 
middle of July. In each region they develop earlier on slopes of 
southern exposure and at lower altitudes. 
The geciospores are discharged in great abundance for a day or two 
and with lessened abundance for about a week longer. They infect 
any Comandra plants with which they come in contact. The leaves 
are most commonly infected, but occasionally the stems and floral 
parts are attacked. The infection near diseased pine is usually very 
abundant, decreasing rapidly as the distance increases. An abundant 
infection from asciospores has not been noted for more than 200 feet 
from the secial center, when it is located on small pines. When large 
pines are diseased in the upper limbs, the distance that the seciospores 
are blown is greatly increased, and the zone of infection is therefore 
extended very much, and on mountain slopes may reach the distance 
of nearly 1,000 feet. This inoculation of Comandra plants by 
83ciospores may well be designated as a primary inf ection, and that by 
urediniospores, described in the following paragraph, as a secondary 
infection. 
In 8 to 10 days from the time of inoculation by reciospores the 
uredinia appear on the leaves of the infected Comandra plants and 
urediniospores begin to be produced. These are blown about by 
winds and inoculate other Comandra plants. This secondary infec- 
tion greatly extends the area of diseased plants. A second crop of 
uredinia develops in from 8 to 10 days from these secondary infections. 
This process continues throughout the growing season. It is possible 
that as many as six or more generations of uredinia may be thus pro- 
duced in one season, and the fungus may spread several miles in this 
manner. It is by this method of infection that the fungus spreads 
the greatest distance in nature, which explains why the form of fungus 
on the Comandra plants is more common than on the form of pines. 
In about 15 days the telial columns develop from the uredinial sori 
on the Comandra plants. As each column grows older it gradually 
elongates, and the development of teliospores progresses outward 
