FUNGI: RUSTS. 135 



the leaves of the barberry, they germinate and produce the cluster cup again. 

 The plant has thus a very complex life history. Because of the presence of 

 several different forms in the life cyle, it is called a polymorphic fungus. 



The presence of the barberry does not seem necessary in all cases for the 

 development of the fungus from one year to another. 



297. Synopsis of life history of wheat rust. 



Cluster -cup stage on leaf of barberry. 



Mycelium between cells of leaf in affected spots. 

 Spermagonia (sing, spermagonium), small flask-shnped bodies 



sunk in upper side of leaf; contain " spermatia." 

 yEcidia (sing, aecidium), cup-shaped bodies in under side of 



leaf. 

 Wall or peridium, made up of outer layer of fungus threads 



which are divided into short cells but remain united. 

 At maturity bursts through epidermis of leaf; margin of 

 cup curves outward and downward toward surface of leaf. 

 Central threads of the bundle are closely packed, but free. 

 Threads divide into short angular cells which separate 

 and become aecidiospores, with orange-colored content. 

 ^Ecidiospores carried by the wind to wheat, oats, grasses, 

 etc. Here they germinate, mycelium enters at stomate, 

 and forms mycelium between cells of the host. 



Uredo stage (red rust) on wheat, oats, grasses, etc. 

 Mycelium between cells of host. 

 Bears uredospores (i -celled) in masses under epidermis, which 



is later ruptured and uredospores set free. 

 Uredospores carried by wind to other individual hosts, and 



new crops of uredospores formed. 



Teleutospore stage (black rust], also on wheat, etc. 



Mycelium between cells of host. 



Bears teleutospores (2 -celled) in masses (sori) under epidermis, 

 which is later ruptured. 



Teleutospores rest during winter. In spring each cell germi- 

 nates and produces a promycelimn, a short thread, divided 

 into four cells. 



