THE RUSTS 233 



substance of the previously healthy cells. After a time 

 this mycelium is ready to produce spores again, and it 

 causes more tiny swellings upon the green surfaces of leaves 

 and stems. The skin of the swollen dots soon breaks apart, 

 revealing swarms of tiny rust-colored spores. These are 

 the uredospores or summer spores. They give the famil- 

 iar rusty color to diseased asparagus plants. They are pro- 

 duced in untold billions, to be scattered by the wind from 

 plant to plant and from field to field. 



When they alight under conditions . favorable to growth, 

 they start the disease anew. These summer spores are the 

 chief means for the general dispersal of the rust. Like 

 the spores produced in spring, they are unable to survive 

 long in a condition to germinate. 



As autumn comes on, if the asparagus host plant becomes 

 weakened from any cause, the mycelium in the leaves and 

 stems produces yet a third kind of spores the black rust or 

 winter spores with which our little story began. These 

 are called teleutospores : they develop in great numbers in 

 swollen pustules, their black color giving this stage the 

 name black rust to distinguish it from the orange rust of the 

 uredospore stage. 



These two-celled teleutospores have comparatively thick 

 walls which enable them to survive the winter and start 

 the disease anew in the spring. 



To summarize this story of the yearly cycle of the As- 

 paragus Rust: 



1. It winters in the black rust or teleutospore stage. 



2. In spring the teleutospores germinate into secondary 



spores called sporidia. 



3. These sporidia infect asparagus plants and start in 



the tissues of leaf and stem a growth of fungus 

 threads or mycelium. 



