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 TXist (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 (aecidiospores) ; D, germinating aecidiospore on wheat; E, 

 wheat plant attacked by aecidiospores 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. 



