10 College of Furesinj 



principally concerned Avitli those changes which distnrb thb 

 normal physiologic processes. 



For several years the black zones fonnd in decaying wood 

 have been a subject of much conjecture. Briefly stated, the 

 problem • resolves itself to this. In the early stages of the 

 decay of dicotyledonous woods by many of the higher fungi 

 known as " polypores/' characteristic blackish zones, limiting 

 various stages of the decay, occur as prominent features of 

 the decomposition. These zones may extend in any direction 

 through the wood or bark, their courses being determined by 

 the initial starting point of the fungus and its subsequent 

 growth and advancement through the wood. Their occur- 

 rence may be observed best on the cross sections of a tree ot 

 log which is but jmrtially decayed. Here they usually appear 

 as blackish or brownish-black lines of varying thickness 

 (Plate 1). Strictly speaking, the term "line" should not 

 be applied to these formations unless used in describing their 

 appearance on a section of wood, since it is only when seen 

 in this manner that they appear as lines. In reality they are 

 thin zones of discolored wood which at first sharply separate 

 the various stages of decay in the w^ood (Plate 1). If, how- 

 ever, tlie decay starts from several centers, so that the decayed 

 areas overlap, the figure becomes complicated and the dark 

 zones extend very irregiilarly throughout the whole mass 

 (Plate 2). The course of the discolored zones of wood is in 

 no way influenced by the course of the growth rings. It 

 usually runs parallel to the direction of the woody elements, 

 although there is considerable variation in this respect. 



]\Iicroscopic examination shows these discolored zones to 

 be caused by brown infiltrations in the cell walls and lumina 

 of the cells. These infiltrations frequently become so 

 abundant that they exude into the lumina of the cells, par- 

 ticularly the vessels, and occlude these completely (Plate 4, 

 Fig. 1). This brown substance usually forms a blackish zone 

 or layer but frequently appears merel}^ as a brown discolora- 



