BEECH-CANKER. 477 



by hard walls. Later on, these blotches become greyish-yellow, 

 and are filled with mycelium. The sporocarps, brownish-yellow 

 incrustations. 



e. Stereum hirsutum, Fr. 



Snow-white or yellow longitudinal bands surrounded by 

 brown tissue appear in the wood,- which is said to be yellow- 

 or white-piped. Sometimes the whole of the wood turns 

 uniformly yellow. The sporocarps, at first mere incrusta- 

 tions, later on assume prominent brown horizontal edges. 

 Common in Britain. 



*3. Nectria ditissima, Tul. 



(Beech-canker.) 

 a. Description and mode of Attack. 



Beech-canker, which may be recognised by the local 

 destruction of the cortex, resembles silver-fir and larch 

 canker. It may be produced on the beech, either by Nectria 

 ditissima, Tul., or by insects (Lachnus exsiccator, Alb., Coccus 

 fagi, Barensp., p. 366), or by frost. The disease is sometimes 

 occasioned by several of these agents. 



The attacks of the fungus may be diagnosed by the local 

 destruction of the cortex, and the appearance of small white 

 tufts of conidiophores ; and later on by dark-red, spherical 

 sporocarps on the canker. The infection always arises at a 

 wound caused by abrasures of bark by felled trees, hail, etc., 

 and from the point of infection the fungus spreads more or 

 less regularly in the wood, but most quickly along the stem. 

 The wood turns brown and dies wherever it is attacked. The 

 diseased portion of the wood appears sunk into the stem, 

 owing to the hypertrophy of the growth of the portions of the 

 stem round the canker. 



Thus the attacked branches and stems become spindle- 

 shaped. The canker becomes every year deeper and more 

 open. 



b. Subjects of Attack, and Distribution. 



The beech-canker chiefly attacks the beech, but oaks, ash, 

 hornbeam, hazel, alder, lime, cherry, maple, and especially 



