The Blacli Zones Formed hy Wood-Destroying Fungi 35 



especially where the advance of the fungus is very slow or 

 ahnost stopped. The portions of the wood thus changed 

 have heen desig-nated as " false (j>athologic) heart." Mlinch 

 (1908, p. 44) is of the opinion that the small supply of air 

 in the interior of the tree as a rule suffices only for a slight 

 growth of the fungus. This causes merely a browning of 

 the wood cells without affecting the woody substance to any 

 great degree. If larger wound surfaces are left unprotected 

 the air in the deeper-lying tissues is constantly renewed 

 (Mlinch, 1908, p. 44). The fungus may then continue its 

 existence and work of decay. Thus the "false heart" is 

 transformed into heart-rot. The sauie author (1910-) states 

 further that the renewing of the air by means of diffusion 

 and diosmosis, which varies according to the greater or less 

 porosity of the wood and from other reasons, plays an im- 

 portant role. Froan this it follows (according tO' Miinch) 

 that the oxygen streaming in from the outside in a radial 

 direction toward the heart or in the intercellular spaces of 

 the pith ray cells is respired by the living sap wood cells, 

 either partially or entirely. Therefore it is merely the re- 

 mainder of the oxygen left after respiration that is available 

 for the fungiis living in the heart. In his opinion more or 

 less oxygen is admitted to the attacked heart, according to 

 the intensity of the respiration, the number of wood cells, 

 etc. Nothing more definite can be ascertained concerning 

 this matter until our knowledge of the vitality of the wood 

 cells is increased.^ 



It is appropriate that the question of what eventually be- 

 comes of the decomposition products as the decay progresses 

 he discussed briefly at this point. The writer has observed 

 frequently in the case of the decay of logs of pignut hickory, 

 IJicoria glabra (]\rill.) Britton, and other woods by Coriolus 

 prolificans (Fries) Murrill, that the decomposition products 



Comiiare the ponclnsions of Miinch (1910'). 



