87 



Effects of the Disease. 



Diseased leaves drop early, so that badly infected trees are bare while 

 the unharmed ones are in full leaf. When the leaf fall is premature the 

 fruit is small or drops unripened. Next spring the fruit buds are weak, 

 and the chances for a crop slight. When the leaves have fallen, the fungus 

 on them fruits and may infect the trunk or the fruit. * 



Black Rot Canker. 



Besides spots on the leaf, the same disease causes cankers on the 

 limbs and Black Rot disease in the growing or stored fruit. While all 

 three forms of the fungus cause serious losses in Quebec, the Canker does 

 most damage. It begins as a shrunken portion of the bark, dark brown 

 or purplish and later blackened by saprophytes. , The bark may be split 

 or cracked, and is soon roughened by numerous dots, the pycnidia, where 

 the bark has burst open to liberate the fruit bodies of the canker. 



Microscopic structure of the fruiting body of the 

 Black Rot Fungus. 



The mycelium grows in the inner and outer bark and scarcely attacks 

 the wood. The inner bark is poisoned and digested by the fungus, and 

 gradually dies to greater or less depth, finally shelling off and exposing 

 the wood. The canker spreads up and down the trunk or limb, gradually 

 girdling it. The smaller branches soon die, other parts more slowly. 

 Through the cankers borers enter the wood, and wood destroying fungi 

 gain a foothold in moist parts where the bark splits and lets in rain. 



