THE HAMILTON ASSOCIATION. 



83 



times two or more spots will coalesce, as it were, forming one large 

 and irregular one. Some- 

 times even the petioles and 

 the young twigs become 

 aifected ; thus in every 

 possible way the fungus 

 tries to rob the tree of its 

 vigor. Fig. 6. 



The most favorable conditions for its growth are the cool, moist 

 weather of spring and fall, while its spread is retarded by the drouth 

 and heat of midsummer. Owing to the dry, warm weather prevail- 

 ing in the early part of last summer, our apples were much freer from 

 scab than usual. 



The fungus appears to retain its vitality during the winter 

 season, being known to spread even in barrels from apple to apple ; 

 and it remains in a living condition through the winter on the twigs 

 of the apples, ready to begin its work of devastation in spring-time. 

 The loss caused to the country is alarming. The Secretary of the 

 Illinois State Horticultural Society places the annual loss due to this 

 parasitic growth at $400,000, but this is very small compared with 

 the annual loss to apple growers in Ontario. 



Fig. 7 shows a section of one of the leaf spots, and fig. 8 a section 

 of the skin of an apple with scab bursting up through the epidermis, 

 or outer skin, both magnified 200 diameters. The mycelium, or 

 plant body of the fungus, resembles a dense mass of tissue composed 

 of dark brown walled cells. These do not penetrate the cuticle, or 



Fig. 8. 



inner skin, but grow between it and the epidermis, or outer skin, 

 which they soon burst open, and send up brown threads on the ends 

 of which are borne the spores for the propagation of the fungus. 



These latter are so tiny, that it would require 3,200, side by 

 side, to reach an inch. They germinate in moisture at a temperature 



