436 



FUNGOUS DISEASES OF PLANTS 



The genus Coleosporium is to be considered entirely heterce- 

 cious, and whenever aecidial stages are known in the life cycle, 

 they occur on species of Pinus, and are referable to the form 

 genus Peridermium. 



The aecidial stage of the species here discussed has recently 

 been found through inoculation experiments to be a form known 



a s Pe ride rmiu m 

 acicolum occurring 

 on leaves of Pinus 

 rigida in several 

 of the northeastern 

 states. The Euro- 

 pean form occurs 

 upon branches and 

 stems of Pinus 

 sylvestris. 



The fungus. The 

 uredo and teleuto 

 stages are merely 

 conspicuous by 

 their color, and in 

 this particular in- 

 stance the aecidial 

 stage is by no 

 means striking. 

 Other forms or 

 species of Peri- 

 dermium, however, 

 may produce considerable swellings upon their hosts. 



According to Clinton the infection of young pine leaves may 

 take place in spring, the aecidia resulting the following year. It 

 would appear that the Peridermium is inessential for the continu- 

 ous propagation of the rust upon composites in the United States, 

 since the uredo stage is produced practically throughout the winter 

 on leaves of the basal rosettes. 



The spermogonia appear upon the needles in autumn, but the 

 aecidia are not developed until spring. They occur on both sur- 

 faces of the leaves in slightly discolored spots, They are crumpent, 



FIG. 212. PERIDERMIUM ON PINE. (After Hartig) 



