PLANT STRUCTURES 



"cluster-cups." This mycelium on the barberry, bearing 

 cluster-cups, was thought to be a distinct plant, and was 



called ^Ecidium. The 

 name now is applied to 

 the cluster-cups, which 

 are called cecidia, and 

 the conidia-like spores 

 which they produce are 

 known as cscidiospores. 



It is the aecidia which 

 give name to the group, 

 and JEcidiomycetes are 

 those Fungi in whose 

 life history aecidia or 

 cluster-cups appear. 



The aecidiospores are 

 scattered by the wind, 

 fall upon the spring 

 wheat, germinate, and 

 develop again the myce- 

 lium which produces the 

 rust on the wheat, and 

 so the life cycle is com- 

 pleted. There are thus 

 at least three distinct 

 stages in the life history 

 of wheat rust. Begin- 

 ning with the growing 

 season they are as fol- 

 lows : (1) The phase bear- 

 ing the sporidia, which 

 is not parasitic ; (2) the 

 secidium phase, parasitic 

 on the barberry; (3) the uredo-teleutospore phase, para- 

 sitic on the wheat. 



In this life cycle at least four kinds of asexual spores 



