324 DISEASES OF ECONOMIC PLANTS 



exceeds that due to any other enemy, insect or fungous, 

 and often equals those from all others combined." ' 



The rust of wheat alone is estimated by Bolley to cause 

 an average loss in the United States of $20,000,000, while 

 Galloway placed the loss in 1891 at $67,000,000. 



The rusts in their most complete form exhibit three dis- 

 tinct stages (cf. asparagus) : the spring stage, or cluster 

 cup, consists of a group or cluster of very minute, cup- 

 like, spore-bearing regions, sori. These cups are sunken 

 in the tissue of the host, often with their rims only pro- 

 truding. The second stage, summer stage, also called 

 the uredo stage, is of entirely different appearance, con- 

 sisting usually of elongated sori, bearing a mass of 

 spores the color of iron rust or verging towards orange or 

 yellow. These spore masses are at first covered by the 

 epidermis of the host, but this covering eventually rup- 

 tures, disclosing the usually dusty or pulverulent mass of 

 spores, surrounded by a fringe of the remaining epidermis. 

 The third stage, winter stage, or teleutospore, consists of 

 sori almost exactly like those of the uredo stage except 

 that the spores within are usually darker in color and in 

 a compact, cushion-like mass, therefore lending to the 

 sorus a considerable alteration in aspect. The sorus is 

 often identical in the two latter stages, a uredosorus grad- 

 ually changing as the season advances into a teleutosorus. 



These three stages have in general three separate func- 

 tions. The function of the teleutospores is to live over 

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

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



• Carleton, M. A., U.S. Dept. Agr. Div. Veg. Phys. & Path. Bui. 16, 

 p. 19, September 27, 1899. 



