INJURIES INDUCED BY PLANTS 



187 



observes only one or a very limited number of diseased spots in 

 a wood, but when these have been allowed to extend for some 

 years one notices new seats of disease establishing themselves all 

 over the wood. 



When the dead trees are examined about the roots, one finds 

 the sporophores, with their snow-white hymenial surface, appear- 



FiG. 119. The sporophores of T. 

 radiciperda on the roots of a 

 spruce. Natural size. 



FIG. 1 20. The mycelium of T. 

 radiciperda on the root of a 

 spruce. The outer bark-scales 

 have been removed from the 

 lower portion so as to show 

 the felted mycelium, a a, while 

 in the upper portion only 

 cushion-like mycelial masses, 

 &, project from between the 

 scales. Twice natural size. 



ing between the bark-scales as very small yellowish-white cushion- 

 like structures (Fig. 119). These coalesce with similar adjoining 

 cushions, and in exceptional cases attain to a diameter of twelve 

 to sixteen inches. In the case of pines the sporophores are 

 usually to be found on the- stool close under the surface of the 

 ground, though sometimes also on the deeper roots, while in the 

 case of the spruce they are almost always to be found only on 

 the roots. Between the bark- scales one finds the ramifying 

 felted mycelium, which is distinguished from that of Agaricus 

 melleus by its extremely delicate texture (Fig. 120). It scarcely 



