The Black Zones Formed hy Wood-Destroying Fungi 81 



been established only for those portions transformed to heart 

 which lie on the enter surface of the wonnded tissue. Here 

 the tyloses and infiltrated decomposition products are most 

 abundant, often in such quantity that an increase in material 

 is evident by mere macroscopic observation. These parts are 

 easily recognized macroscopically by their darker color. They 

 either surround, as '' protection heartwoocl," portions of wood 

 less strongly transformed to heartwood or they bound wound 

 surfaces as '' protection wood." In these cases this zone of 

 " protection wood " is distinguished from the dead wood 

 which it isolates, only by the fact that the tyloses and the 

 oxidation products are more abundant. Hermann (1902) 

 has already mentioned this as occurring in the pathologic 

 heartwood of beech. 



An explanation of this remarkable accumulation of brown 

 material in the uninjured tissues directly underlying dead 

 wood in wounded areas is furnished by the discovery of 

 Miinch (1910\ p. 389). He has pointed out that wherever 

 woody or bark tissues are killed there is an extraordinary 

 movement of formative materials toward the neighborhood 

 of the dead area as a result, so that in such places the cambial 

 activity may be increased several times and additions to the 

 bark may occur beyond the normal. According to the same 

 author the living parenchyma cells in the neighborhood of 

 dead cells have a special attractive force for the formative 

 materials and consequently an increased growth and sub- 

 division may occur, wdiich often is manifested in a prolific 

 formation of tyloses. So, for example, when the fungal 

 hyphae penetrate and consequently kill a portion of the wood 

 an abnormal stream of building materials then flow into the 

 tissues adjoining the dead areas and the parenchyma cells 

 involved develop tyloses. The parts previously rich in these 

 substances are killed likewise by the advancing fungus and 

 its diffusing enzymes. The cell contents are oxidized, after 

 which the transforuiation to pathologic heartwood is complete. 



