112 



N. n. AGR. EXPERIMENT -STATION. 



[Bulletin 142 



greatly reduced before the end of the summer and the possible 

 food supply of the tree similarly decreased. 



It is on the fruit that the fungus produces its most charac- 

 teristic and' serious effects. Here it forms superficial olive col- 

 ored spots known among apple dealers as "scab," ''fungus" or 

 "black spot" (Fig. 2). The spots are usually i/g to 1/2 of 

 an inch in diameter. The mycelium begins its development 

 beneath the cuticle, but soon sends up erect sporophores (spore 



Fig. 2.— Apples affected with scab. (Lamson.) 



stalks j, which break thru to the surface to free their spores. (See 

 A in Fig. 6.) The spores and sporophores give the spot its sooty, 

 olivaceous appearance. The marginal portion of the ruptured 

 cuticle usually remains, giving the spot a light gray border. The 

 fungus checks the growth in the adjacent tissue to such an extent 

 that apples attacked early in the season often become dwarfed 

 and one-sided, and sometimes badly cracked. (Fig. 2.) 



The underlying portions of the apple are protected by the for- 

 mation of a corky tissue beneath the scab spot. This protection 

 is only partial, however, as scabbed apples wither rapidly in 

 storage and the scab spots are quite commonly the point of origin 

 for rots. Even slightly scabbed apples are, therefore, unfit for 

 anything but immediate consumption. 



