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, uredimospores, 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 divaricata) 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 seciospores 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 seciospores 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 

 seciospores may well be designated as a primary infection, and that by 

 urediniospores, described in the following paragraph, as a secondary 

 infection. 



In 8 to 10 days from the time of inoculation by seciospores 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 



