68 



A TEXT-BOOK OF BOTANY. 



months to a year they germinate readily on a culture medium 

 of potato, and retain their power of germination for years 



Rust Fungi. The Rust Fungi are parasitic on higher plants 



FIG. 41. Wheat rust (Puccinia graminis). A, teleutospore or winter spore germinating 

 and giving rise to a promycelium (p) and sporidia (s); B, a few leaves of barberry attacked 

 by sporidia which give rise to the aecidia; C, transverse section through barberry leaf show- 

 ing three cup-like receptacles (aecidia) on the lower surface of the leaf containing per- 

 pendicular rows of conidia (ascidiospores) ; D, germinating ascidiospore on wheat; E, 

 wheat plant attacked by ascidiospores as shown by the elongated blotches on the leaves; 

 F, cross section of leaf of wheat showing on the upper surface the rust spores which are 

 breaking through the epidermal layer (r); G, summer spores (uredospores) ; H, teleutospores 

 or winter spores formed on wheat leaf. After Dodel-Port. 



and produce a thread-like branching, cellular mycelium, which 

 develops in the tissues of the host. They differ especially from the 

 other Fungi in producing resting spores known as TELEUTOSPORES. 



