APPLE DISEASES 



141 



Symptoms. 



The first indication of the disease may appear while the fruit 

 still hangs on the tree, and the symptoms consist in the develop- 

 ment of a smooth, brownish discoloration in the skin. The 

 rotted area increases in size, the general form being retained. 

 The pathogene often comes to the surface and shows itself as 

 grayish tufts (Fig. 37) ; these may be arranged in concentric 

 circles. The rotting of 

 the fruit is finally com- 

 plete (Fig. 37). In 

 many cases the affected 

 fruit becomes jet black 

 and the skin assumes an 

 ebony aspect. Fruits 

 showing such symptoms 

 usually exhibit no ex- 

 ternal signs of fruiting 

 bodies of the causal 

 pathogene. The con- 

 ditions that determine 

 whether an apple affected 

 with the brown-rot dis- 

 ease will remain brown 

 or will become black, as 

 already described, are not well understood. The appearance 

 of these various characters has been explained in relation to 

 weather conditions as follows : (a) if the weather is warm, 

 and the atmosphere has a high relative humidity, the affected 

 fruits become brown, and grayish tufts make an early ap- 

 pearance; (6) if the relative humidity is reduced, the fruit is 

 at first brown, then black, and the tufts are rare or absent; 

 (c) if the air is dry and cool, the affected fruit is black and no 

 grayish tufts develop. In regions where dry air prevails, this 

 type of the brown-rot disease is the more common. Likewise 



FIG. 37. Brown-rot on apple. 



