Fig. lili). Black rust {I'ucrinia gramtnis) 



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

 m, mycelial liypha^ of the rust; ?/. )(, young summer spore, or uredospore ; w, fully 

 formed uredospore; si, upright liyplia upon which uredospore is formed. B, ger- 

 mination of uredospore: kI, old liypha; ii, old uredospore wall ; ni, new mycelial 

 hyphfe. (', winter spore, or teleutospore : st, hypha; t, two-celled spore. D, ger- 

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

 s, spoi-c.s or sporidia. E, section of the barherry leaf showing aridiospore stage 

 of rust: Ci upper cindermi.s, aud e^ lower epidermis; p, wall of cup or Eecidium; 

 0', ajeidiospores. Rearranged fi'om Duggar's "Fungous Diseases of Plants." All 



much enlarged 

 244 



