LARCH-BLISTER. 



455 



similar fungus, D. resinaria, Eehm., attacks chiefly spruces, 

 but also larch. This latter fungus also attacks Pinus excelsa, 

 Wall., and, in America, is very destructive to Abies balsamca, 

 Mill. Both species are wound-parasites, but can enter the 

 tissues of the living tree through wounds made by a minute 

 parasite, Exosporium, the spores of which in damp atmo- 

 sphere can germinate 

 on the cortex of 

 seedlings or young 

 branches. The sporo- 

 carps of Exosporium 

 appear on the surface 

 of the larch as minute 

 black dots and cause 

 cracks in the bark, 

 filled with resin, 

 through which Dasy- 

 scyphaspoi'es can gain 

 admission. 



Dasyscypha caly- 

 cina, Fuckel, causes 

 the destructive larch- 

 blister, of which the 

 symptoms are as 

 follows : Appear- 

 ance of little swellings 

 on the stem and 

 branches, chiefly be- 

 low the crown; the 

 bark splits and tur- 

 pentine exudes, form- 

 ing light grey-coloured patches, and the split increases till the 

 wood is exposed. Little yellowish- white sporocarps of the size 

 of a pin's head appear in the cracks. These are incapable of at 

 once producing fertile spores, and merely wither away if 

 exposed to dry winds. Where they are surrounded by moist 

 air, however, they develop into cup- shaped fructifications, 

 whitish above and pale red below, and these give rise to fertile 

 spores, which infect other trees, The dead parts of the tree 



Fig. 222. Portion of Larch-stem attacked by \Dasy- 



scypha calycina, Fuckel. 

 a Cracks with outflow of resin, b Sporocarps. 



