154 DISEASES OF FIELD & GARDEN CROPS. [CH. 



Fig. 66. Three pustules are farther enlarged to twenty- 

 five diameters in Fig. 78. A reference to Fig. 67, where 

 the pustules of P. Rubigo-vera, D.C., are illustrated to the 

 same scale, will show the difference in size of the sori 

 belonging to the two mildews. The familiar condition of 

 the burst epidermis of the leaf is seen in both, and it is 

 noticeable in P. graminis, Pers., that in bad cases the 

 black pustules commonly become confluent. 



We will now take a transverse section on the line AA., 

 though the smallest of the three pustules illustrated in 

 Fig. 78. If we magnify a thin transparent slice from the 



FIG. 79. 



Transverse section through half a Pustule or Sorus of Puccinia graminis, 

 Pers. Enlarged 200 diameters. 



cut surface 200 diameters as before, we find the limits of 

 the page insufficient for it. One-half the section, there- 

 fore, only is illustrated in Fig. 79, the centre line being 

 shown at AB. If reference is now made to the section 

 through a complete pustule of Puccinia Rubigo-vera, D.C., 

 as illustrated to the same scale in Fig. 68, the difference 

 in size between the two sori will be apparent. The 

 difference in form of the contained teleutospores will be 

 seen when the teleutospores of Puccinia graminis, Pers., 

 Fig. 80, are compared with the germinating teleutospore 



