The Blach Zones Foniwd hij Wood-Desiroying Fungi 11 



tioii in the wood. Wlicii .seen in muss it is responsible for the 

 (lixvk coh^ration mentioned above. At the start the coloring 

 material is a liquid but later dries to a brown amorphous 

 substance. It is presumed that this brown substance consists 

 of decomposition products that have infiltrated into the wood 

 innnediately in advance of the encroaching- mycelium of the 

 fungus. 



In addition to the decomposition products associated with 

 the activities of wood-destroying fungi, the formation of a 

 similar substance has been observed to take place in the tissues 

 of dicotyledonous trees exposed through wounds and as yet 

 free from fungal attack. More recently attention has been 

 called to the formation of similar substances in dead branches 

 and fallen woody parts of dicotyledonous trees, even before 

 they become attacked by wood-destroying fungi. In sucli 

 trees, sections made through the wounds a few days after their 

 fonnation show^ that brownish globules of a giim-like sub- 

 stance occur abundantly in the vicinity of the wounded area. 

 These globules, commonly termed '' wound gum " by the 

 earlier writers, eventually flow together into larger ones whicb 

 fill up the lumina of the woody elements, particularly the 

 vessels, tbereby protecting them to a certain extent against 

 injurious influences. This protective effect, however, is not 

 sufficient for absolute security against the decomposition and 

 decay of the exposed wood. On this account wound diseases 

 are much more likely tO' occur in dicotyledonous trees than 

 in the conifers, for the resin secreted by the latter quickly 

 flows out over the surface of the wound and excludes the en- 

 trance of air and fungi. 



So far as the writer has been able to ascertain, this problem 

 never has been made the subject of an investigation by any- 

 one in this country. The presence of this discoloration is 

 noted invariably in the majority of our descriptions of the 

 decay of dicotyledonous w-oods. Beyond merely noting the 

 occurrence of these zones of infiltrated wood, Imt little has 



