FUNGI: THE RUST FUNGI 



289 



gelatinous substance formed in connection with the teleutospores, 

 which absorbs water and swells. These gelatinous strings of 

 teleutospores are yellow in color. The teleutospores germinate 

 while in the mass, and the sporidia are carried to the apple, to haw- 

 thorns, and other trees where they produce the cluster-cup stage 

 known as apple rust, etc., which occurs both on the leaves and 

 fruit. 



457. 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. 



Fig. 265. 



^Ecidial stage (Roestelia) of Gymnosporangium, showing tube of the cup split into 

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



^Ecidial stage with spermogonia on the barberry. Jicidio- 

 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. Teleuto- 

 spores 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 repre- 

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



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

 example, the hollyhock rust. 



