The Black Zones Formed by Wood-Destroying Fiuigi 27 



ho believes that the twigs lose their moisture too rapidly for 

 the bromiiiig to follow. It is also known in other cases that 

 rapid removal of water prevents browning. The prompt dry- 

 ing of pressed plants obviates the dark coloration ; fruit dried 

 quickly retains its bright color. Miinch (1910-) has stated 

 to the contrary, however, that in many kinds of wood 

 (beech, etc.) no browning occurs even when the drying is 

 gTadual. On the other hand he finds that the browning does 

 not occur if the necessary degree of moisture but insufficient 

 oxygen is present. According to the same authority, wood 

 that is very rich in water and therefore poor in oxygen re- 

 mains uncolored for a long time. The fact follows that the 

 absence of browning is no proof of freedom from fungous 

 attack. 



Bailey (1910) investigated the discoloration of sap wood, 

 or " sap-stain " as it is called commonly, which occurs on 

 freshly cut surfaces of certain dicotyledonous Avoods. He 

 found that when freshly cut surfaces of such woods were 

 exposed to the air under favorable conditions of temperature 

 and moisture a chemical reaction started which, with varying 

 rapidity, produced a colored substance in the wood. The 

 examination of microscopic sections of this sap-stained lum- 

 ber revealed the fact that the colored substance pi'oduced by 

 the chemical reaction was most conspicuously developed in 

 the pith rays and wood parenchyma cells, living tissues 

 which are largely concerned in the storage and conduction of 

 food in the wood. Bailey points out further that in general 

 sap-stain is the result of two agencies : the attacks of fungi and 

 chemical discoloration, the latter being caused in the sapwood 

 by the activity of oxidizing enzymes. That both agencies are 

 closely related to the food substances available in the wood 

 is shown by the fact that the discoloration, whether produced 

 by the activity of fungi or by chemical reaction, is most con- 

 spicuously developed in the pith rays and wood parenchyma 

 cells. In addition both agencies producing sap-stain are de- 



