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637 



known as ' mildew,' produced by the .attacks of the parasitic fungus 

 Puccinia graminis. It was long ago observed that wheat was 

 especially liable to this disease in the vicinity of barberry bushes ; 

 and it is now known that a fungus parasitic on barberry leaves, for- 

 merly known as ^Ecidium berberidis, is the ' ascidiospore ' generation 

 of the same species of which Puccinia graminis is the ' teleutospore ' 



Sfl 



FIG. 475. Puccinia graminis. From De Bary's ' Comparative Morphology and 

 Biology of the Fungi.' (The Clarendon Press.) A, portion of leaf of Herberts 

 with young aecidium; I., section through leaf containing secidia ; sp, spermo- 

 gones; a, iecidia opened ; ^, peridium ; II., group of ripe teleutospores 

 bursting through the epiderm e in leaf of Triticum repens ; t, teleutospores ; 

 III., teleutospores t, and uredospores ur ; I. slightly magnified ; II. x 190; 

 III. x 390. 



generation. The complete cycle of development of the best known 

 Uredinece, such as the mildew (fig. 475), is this. The form known as 

 Puccinia graminis produces teleutospores, thick-walled spores, borne 

 usually in pairs, at the extremity of elongated cells known as basids 

 or steriymata. Each of these teleutospores gives rise, on germinating 

 within the tissue of the grass, to a hypha or promycele, the terminal 

 cells of which develop, on slender basids, each a single spore or 



