The Black Zones Formed by Wood-Destroying Fungi 21 



These brown globules, according to the illustration and 

 description given by Miinch are identical in appearance and 

 cliomical properties with those observed by the waiter in the 

 sapwood of a log of i)ignut hickory, Hicoria glabra (Mill.) 

 Britton, attacked by a common sap-rot fungus, Coriolus 

 prollficans (Fries) Murrill. Eadial sections (10 microns) 

 were made of portions of wood which were in the first stage 

 of decay — that is, tlie wood had been penetrated by fungal 

 hyphae but disintegi-ation had not started. The portions 

 which were sectioned consisted of small resistant areas of 

 wood (Plate 3) left intact after the remainder of the sap- 

 wood of the log was completely decomposed. These areas 

 were sharply demarked from the surrounding, almost com- 

 pletely decayed wood by prominent black zones. In these 

 radial sections almost all of the pith rays contained abundant 

 brown droplets (Plate 4, Fig. 2). 



According to ]\Iiinch the brown substance in the pith ray 

 cells of the poplar twigs examined by him is identical with 

 that spoken of by Frank (1SS-J-) as wound gum and by Th. 

 Hartig (1857) as " Kernstoflfe," since it possesses all of the 

 characteristic chemical properties mentioned by Th. Hartig 

 and Frank and has a similar origin. Miinch finds it to be 

 insoluble and to remain unchanged in water,, alcohol, ether, 

 concentrated caustic potash, concentrated sulphuric acid (in 

 which the wood SAvelled up and became darker), and cold con- 

 centrated nitric acid. In boiling concentrated nitric acid 

 he observed that the brown substance quickly dissolved to a 

 colored solution. The latter reaction had been reported 

 earlier by Th. Hartig (1. c), who had first studied the sub- 

 stance. 



Frank (1884, p. 324) in describing the characteristics of 

 wound g-um states that if a cross section of such infiltrated 

 wood be digested for a quarter of an hour with dilute hydro- 

 chloric acid and potassium chlorate the gilmmy substance is 

 converted into a new^ compound which, while likewise in- 



