LAKCH-CANKEJ:. 241 



trees canker-spots may dry up and become partially cicatrised, 

 but the diseased part is spoiled as timber. 



The first signs of disease are smooth shining spots or 

 swellings on the stem or branches ; then the bark splits, a slight 

 outflow of resin takes place, and bits of bark scale off, while 

 small cup-shaped sporophores with felty white or grey edges 

 and bright orange-red or pinkish-yellow centres appear. The 

 dead parts grow scurfy and black, while the wounds deepen as 

 the bark curls up at the edges, and gradually spread up and 

 down, or else round the stem, thus killing the pole or the 

 crown above the wound. 



Remedy. As infected stems or branches spread the disease, 

 diseased poles should (if practicable) be cut and removed from 

 the woods. The cleaner that plantations are kept, and the 

 more regularly they are thinned, the less favourable are the 

 conditions for the fungus. Pure Larch plantations are almost 

 certain to be more or less attacked, and the only way of 

 securing even partial immunity is to grow Larch in admixture 

 with broad-leaved trees (Beech, if possible). Mixing Spruce 

 and Larch is more likely to spread than to prevent the disease 

 (owing to Chermes abietis-laricis, see p. 226). 



P. resinaria produces a similar disease on Spruce and Pinus excelsa in 

 southern England, and also on Larch, and is only distinguishable by its 

 cup-shaped sporophore being paler in colour, smaller, and more distinctly 

 stalked. 



Phoma pithya attacks twigs and branches of Douglas Fir and Pine, 

 destroying the bark and producing constriction round the stem, which 

 dies above if the cambium is destroyed right round, but heals by 

 cicatrisation if the stem has not been completely ringed. Infection 

 usually takes place where branches join the stem. Ph. abietina does 

 similar damage to Silver Fir twigs and branches. Septoria parasitica 

 often kills the leaders of common and Menzies Spruces from seedlings up 

 to 30-year-old poles, young shoots infected at their base drooping in May 

 or June, then withering and dying within 7 to 14 days. 



The Silver Fir needle-blight, Trichosphwria parasitica, often in damp 

 localities attacks young poles and lower branches of Silver Fir, Spruce, 

 and Douglas Fir, and makes the leaves turn brown, when they hang down, 



Q 



