1 8 4 



Larch and Spruce Canker. 



of larch canker ; nevertheless, with practice 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 original 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 resin 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 consider- 

 able 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 by 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 balsamed) 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 trunk 

 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 secondary cortex. Wounds caused by insects and by 

 hail and by the breaking of the branches by snow and ice, also 

 expose the cambium to the fungus spores." 



The ascophore or cup of the fungus in D. resinaria is some- 

 what smaller than in D. calycina, more distinctly stalked, and 

 with a yellow or pale orange, not orange-red disc ; externally 

 white or tinged grey, minutely velvety under a pocket-lens. 

 Conidial form minute, dull orange. (Fig. 4, PI. I.). The 

 essential specific characters of the present species are the very 

 minute, subglobose spores, averaging 3 x 2 — 2*5 /x. ; conidia 

 elliptic-oblong, 2 X I >. 



