2.S2 



I'LAKT STTDIES 



"cluster-Clips." This mycelium on tlie barberry, bearing 

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



called jHcidium. The 

 name now is applied to 

 tlie cluster-cups, which 

 are called wridia, and 

 the conidia-like spores 

 which they produce are 

 known as (prii/io.sjxires. 



It is the a^cidia which 

 give name to the griiu}i, 

 and ^Ecidioniycetes are 

 those Fungi iii wliose 

 life liistorv a^eidia or 

 cluster-cu])s apjjear. 



The a^i-idiosjii.ires are 

 scattered by the wind, 

 fall ujion the spring 

 wheat, germinate, and 

 develop again the m)r(.'e- 

 lium which produces tlie 

 rust on tlie wheat, and 

 so the life cycle is com- 

 pleted. There are tlius 

 at. least three distinct 

 stages in the life history 

 of wheat rust. Begin- 

 ning with the growing 

 season they are as fol- 

 lows : (1 ) 'I'he phase bear- 

 ing the spovidia, which 

 is not parasitic; ("2) the 

 " a'cidium pliase, parasitic 



on tlie bai'lu'rry; (.'!) the uredo-tcleutospore ])hase, para- 

 sitic on the wheat. 



In this life cycle at least four kinds of asexual spores 



