66 



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 cecidiospores. 



It is the a3cidia which 

 give name to the group, 

 and ^Ecidiomycetes are 

 those Fungi in whose 

 life history ascidia 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 

 aecidium 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 



