GROUPS OF PLANTS. 



37 



Wheat Rust. — The most important member of the Rust 

 Fungi is Puccinia, of which there are a large number of species 

 that are destructive to economic plants as wheat, plum, cherry, 

 red currant, etc. The one whose life history has been best 



Fig. 24. Wheat rust (Puccinia graminis). A, teleutospore or winter spore germinat- 

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

 attacked by sporidia which give rise to the secidia; C, transverse section through bar- 

 berry leaf showing three cup-like receptacles (secidia) on the lower surface of the leaf con- 

 taining perpendicular rows of conidia (secidiospores) ; D, germinating Kcidiospore 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. 



studied is the wheat rust {Puccinia graminis), which requires 

 two different plants to complete its life history, namely, wheat 



