32 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



About three months after inoculation the fruit of the 

 E;cosporium appears on the surface of the bark under the form 

 of numerous minute black dots, as seen by the naked eye. 

 About this time the bark of the branch in the neighbourhood of 

 the fungus becomes cracked, and the cracks, which always remain 

 narrow, are filled with resin. It is through these resin-filled 

 cracks that the germinating spores of Dasyscypha resinaria find 

 their way into the interior of the living tree. 



In addition to the cracks made by Exosporium, the Dasyscypha 

 spores germinate on resin oozing to the surface through wounds 

 caused by Chermes abietis, L., or by various mechanical injuries, 

 similar to those mentioned under larch canker. 



The general appearance of spruce canker is similar to that 

 of larch canker ; nevertheless, with pi'actice it is possible to 

 distinguish between the two, by naked eye characters. 



Soon after infection the outer bark is broken up into fragments 

 which fall away, owing to the pressure exerted by the rapidly 

 growing inner bark, which becomes hypertrophied. With age the 

 oricfinal depression in the bark caused by the fungus increases in 

 size, but there is more swelling round the edges of the wound 

 than is the case in larch canker, and the wound is more inclined 

 to completely girdle the branch attacked. The flow of i-esin is 

 much more copious than in larch canker, and large gum-pockets 

 are formed in the wood, filled with hardened resin, which on 

 examination is found to be permeated with the mycelium of the 

 parasite. Resin canals are formed in considerable numbers in the 

 wood near the wound, and the resin also often fills the cells lining 

 the resin canals. 



In the United States the injury done V)y Dasyscypha resinaria 

 appears to be much more serious than it is with us at present. 

 It is thus described by Anderson (6) : — " On some trees {Abies 

 balsamea) almost every knot and dead branch was surrounded 

 by one or more of these canker swellings, the canker not 

 infrequently extending all around the tree tnink or branch. 

 When younger stems or branches were affected in this way, 

 the portion above the canker, and often the whole stem, had 

 been killed by the girdling. . . . Infection takes place, as a 

 rule, around the base of the imperfectly self-pruned branches of 

 the lower part of the trunk. At these places the spores gain 

 access to the inner living bark and to the cambium, where they 

 germinate and cause the increased growth of the wood and 



