Minnesota Plant Diseases. 



161 



mycelium of the fungus. The cups are at first closed and then 

 resemble small spheres ; the walls later open at the summit, roll 

 back and expose the spores as an orange-yellow dust. The 

 spores are formed in chains which arise in a pal'sade from the 

 floor of the cup and are formed continuously for some time, 



fied. After Tavi-1. 



those at the summit being the first to mature. These cluster- 

 cup spores are ball-shaped or have flattened sides and their 

 outer wall is frequently provided with small warty roughnesses. 

 The cluster-cup spores are blown about by the wind and are 

 capable of immediate germination. When germinating they 



send out a germ thread which causes infection. Accompanying 

 ii 



