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MANUAL OF TREE DISEASES 



of spore (the ascospores). These spores are confined in small 

 delicate sacs, eight spores in each sac or ascus. During rainy 

 periods, these sacs swell and a certain number are forced up 



through a tube leading from each 

 cavity to the black mouths at the 

 tips of the papillae. Once out- 

 side, the sacs burst and the eight 

 spores in each are shot into the 

 air where they are carried away 

 by the wind to great distances. 

 It is these wind-blown ascospores 

 which account for the extreme 

 rapidity of spread of this fungus 

 and make certain the infection of 

 all trees in the vicinity. 



The living tissues of the bark 

 and the cambium are killed and 

 the mycelium enters the first layer 

 or two of the sapwood. The 

 indirect effect, when these tissues 

 are killed entirely aroimd a limb, 

 is the withering and dying of the 

 parts above. The tree is thus 

 killed by the successive girdling 

 of the limbs and finally by cankers 

 developing on the trunk. 



Fig. 20. — Perithecial stage of 

 chestnut canter fungus. 



Control of Endothia canker. 



After the chestnut canker had 

 developed into a destructive 

 epiphytotic in Connecticut, New York, New Jersey and Penn- 

 sylvania, many investigations were begun to determine the 

 facts with regard to the disease and especially with a view 

 toward its control. A method was proposed of eliminating 



