st 



FIG. 199. Black rust (Puccinia graminis) 



A, A small section of a wheat leaf upon which the parasitic rust is growing: 

 ra, mycelial hyphse of the rust; y. i(, young summer spore, or uredospore; u, fully 

 formed uredospore ; st, upright hypha upon which uredospore is formed. B, ger- 

 mination of uredospore : st, old hypha ; u, old uredospore wall ; m, new mycelial 

 hyphae. C, winter spore, or teleutospore : st, hypha; t, two-celled spore. D, ger- 

 mination of teleutospore: st, old hypha; p, new hypha, or the promycelium; 

 s, spores or sporidia. E, section of the barberry leaf showing secidiospore stage 

 of rust: ej upper epidermis, and e z lower epidermis; p, wall of cup or aecidium; 

 s, secidiospores. Rearranged from Duggar's "Fungous Diseases of Plants." All 



much enlarged 

 244 



