276 Diseases of Economic Plants 



bearing regions. These cups are sunken in the tissue of the 

 host, often with their rims only protruding. The second, or 

 summer, stage, also called the uredinial stage, is of entirely 

 different appearance, consisting usually of elongated sori, 

 bearing a mass of spores the color of iron rust or verging 

 toward orange or yellow. These spore masses are at first 

 covered by the epidermis of the host, but this covering 

 eventually ruptures, disclosing the usually dusty or pul- 

 verulent mass of spores, surrounded by a fringe of the re- 

 maining epidermis. The third, winter or telial, stage consists 

 of sori almost exactly like those of the uredinial stage except 

 that the spores within are usually darker in color and in 

 a compact, cushion-like mass. The sorus is often identical 

 in the two latter stages, a uredinium gradually changing as 

 the season advances into a teliuni. 



These three stages have, in general, three separate func- 

 tions. The function of the teliospores is to live over winter 

 or over the long resting period of the fungus. They are 

 essentially long-lived and hardy. The cluster-cup spores 

 multiply and spread infection, especially in the earliest part 

 of the season. The urediniospores continue the multiplica- 

 tion and infection throughout the growing season of the host. 

 The last two forms of spores are in general comparatively 

 short-lived. If the host plant remains alive over winter, as is 

 the case with winter wheat, the fungus, in the South, may 

 continue to grow and produce summer spores throughout 

 the winter. Even in colder climates the urediniospores 

 of some rusts live over winter and start infection in the 

 spring. 



In the case of some rusts these three forms are all known 

 to be present. In the case of other rusts one stage or even 

 two stages may either be unknown or may not exist at all. 

 When all three stages do exist, the spring stage often develops 

 upon some host other than that bearing the uredinial and 

 telial stages. Thus the spring stage of the wheat rust is 

 found upon the barberry; of corn upon oxalis; of oats upon 

 buckthorn. 



