6 



N. H, AGR. EXPERIMENT STATION. 



[Bulletin 157 



the end of the summer and the food supply of the tree simi- 

 larly decreased. 



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

 istic and serious effects. Here it forms superficial olive colored 

 spots known among apple dealers as "scab," "fungus" or "black 

 spot" (Fig. 2). The spots are usually 1-8 to 1-2 of an inch in 

 diameter. The mycelium begins its development beneath the 

 cuticle, but soon sends up erect sporophores (spore stalks), 

 which break thru to the surface to free their spores. (See A 

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



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



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 

 formation of a corky brown tissue beneath the scab. This pro- 

 tection is onh^ i^artial, 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. 



