Larch and Spruce Canker 



185 



Both ascospores and conidia germinate freely when placed in 

 contact with a thin section of cortex or wood of the host-plant 

 in a hanging drop. 



Successful inoculations resulting in theproduction of ascophores 

 have resulted from introducing a fragment of mycelium enclosed 

 in resin into punctures in larch 'and spruce. Ascophores also 

 followed the placing of ascospores in the minute cavity occupied 

 "by Chermes laricis on Larix sibirica, Ledeb. 



In addition to Dasyscypha calycina and D. resinaria, certain 

 other species belonging to the same genus, and bearing a close 

 superficial resemblance to D. calycina, occur on various 

 conifers ; and judging from the appearance of the wound 

 produced, may be considered as wound-parasites. 



Dasyscypha subtilissima, Cooke, has been observed on Abies 

 pectifiata, D.C., and Larix curopcea, D.C., in Britain, France, 

 Germany, and the United States. 



Dasyscypha calyciformis, Rehm, has been shown by Wagner (7) 

 to be parasitic on Pinus silvestris, L., Abies pectinata, D.C., and 

 Picea excelsa, Link, in Germany. 



Probably the North American Dasyscypha Agassizii Sacc, 

 growing on Abies sp. should be included here. 



Summary. 



The larch is most susceptible to canker when quite young, 

 and as the fungus spores in the majority of instances gain an 

 entrance to the living tissues through injuries caused by the 

 larch aphis Chermes laricis, Hedwig : it follows that seedlings 

 and young trees should be protected against this pest. This can 

 be accomplished by spraying in the spring with paraffin emulsion, 

 prepared as follows :— Dissolve half a pound of soft-soap in 

 two gallons of hot water, then add two gallons of paraffin 

 and mix thoroughly until the ingredients do not separate on 

 standing. One gallon of the emulsion thus prepared should 

 be diluted with fourteen gallons of water, when it is ready 

 for use. 



Recent investigations tend to show that the spruce-gall aphis 

 {Chermes abictis, L.), and the larch aphis (Chermes laricis, 

 Hartig), are alternating stages of one species. The sexual 

 generation occurs only on the spruce, the agamic generations, 



