456 PROTECTION AGAINST FUNGI. 



turn black, and owing to the swelling of the walls of the 

 canker and the local stoppage of the growth, its centre 

 forms a spoon-shaped depression, and the canker itself is 

 spindle-shaped. Several cankers may appear on the same tree. 



The fungus can gain admission only through wounds, 

 frequently of brachyblasts eaten by Coleophora laricella, Hbn. 

 (vide, p. 846), punctures made by Che.rmes (pp. 361 364), or 

 due to snow-break, etc. After the entrance and sprouting of 

 the spore the richly-branching mycelium traverses the bast, 

 but only during the spring, as its further progress is cut off by 

 the formation of corky tissue separating the diseased place from 

 the still healthy bast. The exposed wood exudes turpentine, 

 and in the autumn the mycelium grows again from the cambium 

 into the healthy bast and increases the size of the canker. 

 Fresh layers of cork again cut it off, and the growth of the 

 mycelium is repeated, a protracted contest between the tree 

 and the fungus usually ensuing. In the Tyrol, a living larch 

 tree has been seen affected by a canker 100 years old. 



When the canker is small and the growth of the larch 

 vigorous, on account of the locality being suitable for it, the 

 damage done is limited to the point of attack. When, however, 

 the parasite grows fast and the growth of the tree is not 

 vigorous, the mycelium may penetrate the wood by the 

 medullary rays even down to the girth, and the flow of sap is 

 seriously interrupted. The tree then begins to languish, 

 needles turn pale, twigs dry up and die, while fresh cankers 

 develop, especially in damp places. In such localities the 

 cankers may be of reduced size, but the mycelium spreads 

 throughout the wood, and the sporocarps appear in all directions 

 on the bark. 



b. Subjects of AtfarJc, and Distribution. 



D. calycina, Fuckel, attacks Larix europaca, D.C., wherever 

 it grows. It occurs in Britain, also, on Scots pine, mountain 

 pine and silver-fir. Japanese larch, L. Lcptolepis, Gord., has 

 also been attacked (Berlin, 1895, Hennings). 



The larch-blister or canker is found in localities which differ 

 widely from one another, but is most prevalent in damp places 

 with moist air and in frosty and cloudy localities. The 



