FUNGI, THE RUST FUNGI 



319 



472. Life history of the wheat rust. The complete life 

 history of the wheat rust described above in abbreviated form is 

 as follows, remembering that the mycelium or plant is present in 

 all spore forms except in the formation of the sporidia on the 

 promycelium. 



^Ecidial stage with spermogonia on the barberry. ^Ecidio- 

 spores carried to the grasses and cereals. Uredo stage with 

 repeated crops of uredospores, the uredo stage being the propa- 

 gative stage, mycelium finally producing teleutospores. Teleu- 



Fig. 279. 



jEcidial stage (Roestelia) of Gvmnosporangium, showing tube of the cup split into numerous 

 slender divisions which are recurved against the leaf. On leaves of Crataegus. 



tospores after a period of rest* produce a promycelium from each 

 cell with four sporidia. The sporidia pass to the barberry, infect 

 it, produce mycelium which gives rise to more spermogonia, 

 aecidia and aecidiospores. The cycle of the life history may be 

 represented by the diagram III A, and in diagrams B, C, D are 

 shown in the life cycles of rusts having fewer spore forms. For 

 example, some lack the uredo stage, as in Puccinia podophylli on 

 the mandrake ; others lack the aecidial stage, as in Puccinia tarax- 

 aci on the dandelion; while still others lack both aecidia and 



* In some species the teleutospores germinate as soon as they are mature, 

 example, the hollyhock rust. 



