84 MANUAL OF GENEEAL AGEICULTURE. 



On the Leaves. The first evidence of the disease in 

 the spring is upon the unfolding leaves. The scab spots 

 usually appear first upon the under surface. Later the 

 upper surface Becomes infected. Examine the leaves pro- 

 vided and observe : 



1. The size, form and character of the spot. The 

 radiating character of the markings of the lesion. To 

 what due ? 



2. The character of the injury to the leaf. Does the 

 injury show on the surface opposite the spot ? 



3. Difference in the character of the upper and un- 

 der surface of the leaf itself. Of the scab spots on the 

 two surfaces of the leaf. 



4. The variation in the character of the scab spots 

 on different leaves. Make drawings to show the charac- 

 ters of the scab spots on the upper and under surface of 

 the leaves. 



On the Fruit. Where the infection of the calyx is not 

 severe enough to prevent the fruit from setting, the apple 

 as it enlarges shows the enlarging scab spots which be- 

 come very evident as the season advances. In the young 

 apples provided. Observe : 



5. The black scab spots. Their form, size and effect 

 on the fruit. To what region on the apple are they largely 

 confined ? Why ? 



6. The f elty black center of the spot. In some cases 

 this felt is gone at the center of the spot, which is hard, 

 of a reddish brown color and often cracked. 



7. The papery rim of border of the spot. Best seen 

 in the younger spots. This consists of the cuticle of the 

 apple that had pried loose by the fungus as it spreads out 

 from the center of the spot. Make drawings to show the 

 points brought out in 5, 6 and 7. 



Sometimes these spots cause a dwarfing of the apple 

 on the affected side so that they become one sided. 



The apple scab is caused by the fungus known as 

 Venturia inequalis. It lives upon the surface of the host 



