10 BULLETIN 191 



dition is, shown clearly in Figure 1, which is a longitudinal section of 

 a diseased pine, cut squarely through the center of the knot. It will 

 be noticed that the fungous growth is present in the vicinity but does 

 not penetrate this resinous wood of the old branch. 



Morphological characters; wood dissolution. The visible effects 

 of the growth of the fungus in the wood are described by Von 

 Schrenk (2) for spruce in part as follows: "The first effect to be 

 noticed is a change in the color of the. wood from natural light straw 

 color to a purplish gray. Very sflon this gray deepens to a red brown. 

 Black lines precede the appearance of small white areas. These areas 

 usually are some distance from each other and are arranged longi- 

 tudinally (Plate II). Some of the holes fill with a mass of white fibers. 

 As the holes grow in number and size they appear to unite longitudinal- 

 ly rather than radially. As the disease advances in the tree, the 

 destroyed cells fill with a dark brown mass of hyphae 1 . These hyphal 

 plugs occur in nearly every tracheid and are accompanied by a brown 

 incrustation which dissolves in part in dilute potassium hydroxid and 

 entirely in warm nitric acid. These incrusting substances apparently 

 were decomposition products and were laid down in liquid form. 



"The changes in the cell walls resulting from the attack of the 

 mycelium are fully described by Hartig (1). There is a gradual ex- 

 traction of those elements which give a lignin 2 reaction due to the 

 probable secretion by the fungus of lignin-dissolving enzyms. 3 This be- 

 gins in the tertiary lamella and proceeds outward slowly through the 

 secondary lamellae. The primary lamella splits at this state and dis- 

 solves, leaving the individual tracheids entirely free from each other and 

 composed approximately of pure cellulose. The white spots are the 

 points at which the change to cellulose has taken place. Preceding the 

 change of the wood fiber to cellulose, the wood is filled with masses 

 of hyphae which become masses in centers and bring about the dis- 

 solution of the wood. 



"The hyphae grow out from the original centers in all directions, 

 proceeding faster up or down the stem parallel to the tracheids than 

 they do across them. It is the opinion of the writer that the decom- 

 position products cause the destruction of the wood to stop at this 

 point. In the newly invaded trunks the mycelium is colorless. The 

 hyphae are somewhat thick walled and have numerous short branches 

 which penetrate the walls in all directions." 



1 The term "hyphae" as used here, is synonymous with mycelia. 



2 The woody substance of the cell wall. 



3 An enzym is a ferment possessing the power to decompose organic compounds. 



