x.] "CANKER": THE LARCH DISEASE. 233 



destroyed, the general effect is eventually to " ring" 

 the tree. 



To understand these symptoms better, it is 

 necessary to examine the diseased patch more 

 closely in its various stages. The microscope shows 

 that the dead and dying cortex, cambium, and 



FIG. 35. Porti n of stem of a young larch affected with the larch disease, as indicated 

 by the dead " cancerous " patch of cracked cortex, a : at and near the margins of 

 the patch are the small cup-like fructifications of Peziza Willkommii(H.\.g.'), which 

 spring from mycelium in the dead and dying cortex and cambium beneath. (After 

 Hess.) 



young wood in a small patch, contain the mycelium 

 of the fungus which gives rise to the cup-like 

 fructifications Peziza Willkommii above referred 

 to (Fig. 35); and it has been proved that, if the 

 spores of this Peziza are introduced into the cortex 



