P 



FIG. 198. Wheat rust (Puccinia graminis) 



A, part of a wheat plant showing rust spots on the stalk. B, a small section of a 

 wheat leaf upon which the parasitic rust is growing: m, mycelial hypha? of the 

 rust; y.u, young summer spore, or uredospore; u, fully formed uredospore; st, 

 upright hypha upon which uredospore is formed. C, germination of uredospore: 

 st, old hypha; u, old uredospore wall ; m, new mycelial hyphae. D, winter spore, 

 or teleutospore : st, hypha ; t, two-celled spore. E, germination of teleutospore (t) : 

 st, old hypha; p, new hypha, or the promycelium; s, spores, or sporidia. F, sec- 

 tion of the barberry leaf, showing a3cidiospore stage of rust : e^ upper epidermis, 

 and e 2 lower epidermis; p, wall of cup, or secidium; s, secidiospores. All much 

 enlarged. Rearranged from Duggar's " Fungous Diseases of Plants " 



255 



