68 



MANUAL OF TREE DISEASES 



only partially decayed wood. Another common distingulsli- 

 ing mark which may accompany wood-decay is the production 

 of black lines or discolored zones which usually mark the place 

 where the most active changes are occurring in the deligni- 

 fication process. The colored zones are due to dark colored 



oxidation products which 

 stain the mycelium and 

 cell-walls of the wood. 



The mycelium of wood- 

 rotting fungi uses the 

 dissolved wood-tissue as 

 food material. After a 

 considerable amount of 

 this food is obtained and 

 stored, the production of 

 the fruiting-bodies be- 

 gins. For this puirpose 

 a tissue-like development 

 of closely tangled my- 

 celium, in the shape of 

 a knob, usually forms at 

 the original point of in- 

 fection. The food ma- 

 terials from all directions 

 are transported to this 

 point and the fruiting-body develops an upper sterile surface and 

 a fertile suspended layer of spore-bearing tissue on the upder 

 surface. In the case of the toadstools the spores are borne on 

 the sides of pendent plates or gills (Fig. 8, page 81), and in 

 the bracket-fungi or polj^jores, they are borne on the inner sur- 

 face of perpendicular tubes which are open at the lower end 

 and are visible to the naked eye. as small holes in the lower 

 surface of the fruiting-body (Fig. 5) .iL Besides the character- 

 istic action of the mycelium of the different species of fungi 



Fig. 5. — Under surface of a polypore, show- 

 ing open ends of spore-bearing tubes. En- 

 larged (several times). 



