152 TIMBER AND SOME OF ITS DISEASES. [CHAP. 



of the fungus first begin to enter the wood, they grow 

 upwards more rapidly than across the grain, piercing 

 the walls of the cells and tracheides by means of a 

 secretion a soluble ferment which they exude. 

 This ferment softens and dissolves the substance of 

 the walls, and therefore, of course, destroys the struct- 

 ure and firmness, &c., of the timber. Supposing the 

 filaments to enter cells which still contain protoplasm 

 and starch, and other nutritive substances (such as 

 occur in the medullary rays, for example), the fila- 

 ments kill the living contents and feed on them. The 

 result is that what remains unconsumed acquires a 

 darker colour, and this makes itself visible in the mass 

 to the unaided eye as a rosy or purple hue, gradually 

 spreading through the attacked timber. As the de- 

 structive action of the fungus proceeds in the wood, 

 the purple shades are gradually replaced by a yellowish 

 cast, and a series of minute black dots make their 

 appearance here and there, then the black dots 

 gradually surround themselves with the white areas, 

 and we have the stage shown in Fig. 1 3. 



These white areas are the remains of the elements 

 of the wood which have already been completely 

 delignified by the action of the ferment secreted by 

 the fungus filaments i.e. the hard woody cell-walls 

 have become converted into soft and swelling cellulose, 



