144 DISEASES OF FIELD & GARDEN CROPS. [on. 



spheres burst through the cuticle of the host plant gener- 

 ally from the under side of the leaves, and often through 

 the stem. As the JEcvdvwm cups mature they burst at the 

 exposed apex, and the fractured part turns back so as to 

 give the little fungus growths the form of minute cups 

 filled with spores. 



The under side of a leaf of Tuberous Comfrey, Sym- 

 phytum tuberosum, L., is illustrated, natural size, at Fig. 

 70. Two groups of the cups belonging to 



x-io 



FIG. 70. 

 Leaf of Tuberous Comfrey, Symphytum tuberosum, L., invaded 



asperifolii, Pers., natural size. 

 jficidium cups at B enlarged 10 diameters. 



asperifolii, Pers., are shown at AA. Each cluster of 

 cups is surrounded by a large pallid disease patch, which 

 has been caused by the exhaustion of the vital material of 

 the leaf by the spawn of the fungus which at first grew 

 within. The fungus growth has also caused the leaf to 

 become torn. Five of the little AZcidium cups are shown, 

 enlarged to ten diameters, at B. 



At A, Fig. 71, one of the mature Medium cups is 

 farther enlarged to fifty diameters ; the cup has burst, and 



