Larch and Spruce Canker. 



183 



has been generally considered that the last-named disease was 

 always due to the presence of DasyscypJia calycina, it is quite 

 probable that DasyscypJia resinaria is frequently passed over as 

 D. caly cina. 



In this country D» resinaria is most frequently met with on 

 the spruce {Picea excelsa, Link), and has occurred in Shropshire, 

 Yorkshire, Surrey, and Hants. It is also not uncommon on the 

 larch {Larix europcea, D.C.), where it occurs either alone or in 

 company with D. calycina. Quite recently D. resinaria has 

 proved very destructive to the Bhotan pine (Pinu's excelsa, Wall.) 

 in Wiltshire. 



On the Continent D. resinaria has been recorded from 

 Germany and Hungary, a parasite on the spruce fir ; whereas 

 in the United States this fungus causes great injury to Abies 

 balsamea, Mill. 



Like D. calycina, D. resinaria is a wound parasite, and is 

 frequently enabled to enter the tissues of a living tree through 

 wounds made by another minute parasitic fungus, a species of 

 Exosporiuvi (Figs. 20 — 25). 



I have proved by carefully-conducted inoculation experi- 

 ments on seedling spruce, that the Exosporium is a true parasite ; 

 its spores, when placed on the open bark of seedlings or the 

 young branches of old trees, can germinate and pierce the bark 

 and pass into the inner actively-living tissues, provided the 

 atmosphere remains damp, until the spores have germinated and 

 t he germ-tube passed into the interior of the branch. 



About three months after inoculation the fruit of the 

 Exosporium appears on the surface of the bark under the form 

 oi 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 DasyscypJia resinaria find 

 their way into the interior of the living tree. 



In addition to the cracks made by Exosporium, the DasyscypJia 

 spores germinate on resin oozing to the surface through wounds 

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

 similar to those mentioned under larch canker. 



The general appearance of spruce canker is similar to that 



