XXIII.] 



SUMMER EUST AND MILDEW. 



153 



following manner : As the summer advances the rust 

 mycelium within the leaf of the wheat plant gradually 

 ceases to produce rust spores, and, instead, produces dark 

 brown or blackish spores jet black 

 to the unaided eye. A fragment of 

 a wheat stem is illustrated at Fig. 

 77, enlarged five diameters ; the 

 jet black pustules here shown repre- 

 sent the genuine corn mildew of 

 agriculturists, and this perfect con- 

 dition of the disease is the Puccinia 

 graminis, Pers., of botanists. The 



X 5 



FIG. 77. Fragment of Wheat 

 stem invaded by Puccinia 

 graminis, Pers. Enlarged 

 5 diameters. 



X-25 



FIG. 78. Pustules or Sori of Pucdnia 

 graminis, Pers. Enlarged 25 dia- 

 meters. 



black disease spots are much larger in P. graminis, Pers., 

 than in P. Rubigo-vera, D.C., as may be seen by referring to 



