588 



I>li<^ht may often lie proved also on the liranches and twigs on which 

 occur canker excrescences. In all three varieties of injury a bright red to 

 brown, flat conical, or oval fruit body of Nectria dilissima may be found, 

 not infrequently, in winter on the dead, cracked edges of the wound. 



If a cross-section is made througli the excrescence of a closed canker, 

 approximately the following i)icture is found. 



We see (Fig. 135) the whole large swelling divided radialh' into two 

 groups by the split (sp) with its roll-like edges. This cleft forms the inner 

 continuation of the outwardl}- recognizable funnel-like depression on the 

 flattened toj) oi the canker excrescence ( b'igs. 134, 135 /). At the bottom 



Fi{?. ]3i). Cross-sec-tion through ;in apple b 



met of "closed ranker." 



of the cleft usually lies a brown, mealy, or putty-like mass which is found 

 to consist of humified cell remnants. The edges (r) of the cleft are also 

 strongly browned. They arc formed by thick-walled, parenchymatous-like 

 porous cells, provided with a dead, brown content. The further back one 

 goes from the edges of the cleft, or the point of dying, toward the healthy 

 tissue of the trunk, the less noticeable is the brown color. The tissue be- 

 comes white and is formed of parenchymatous wood which contains an 

 unusual amount of starch, (jroups of strongly refractive cells gradually 

 appear in these masses of parenchyma wood. They are clearly elongated, 

 thick-walled wood cells which, isolated at times, or in small groups, appear 

 irregularly distributed in the parenchymatous wood. (Fig. 135 h). Com- 



