34 



The parts of the primar}^ lamella which are situated between three or 

 more cells resist longest (PI. IX. fig. d,j)) and can be found free between 

 the white cellulose fibers. The change to cellulose apparently takes 

 place simultaneously over a considerable area. The first evidence of 

 this change is to be seen in the white spots which come after the black 

 lines. The white spots are the points at which the change to cellulose 

 has taken place. The cellulose fibers are absorbed later on, giving rise 

 to the holes already mentioned. Preceding the change from wood 

 fiber to cellulose the wood is full of hj^phae, which become massed in 

 centers here and there and bring about the dissolution of the wood. 

 It is as yet undetermined what causes influence this local initiation of 

 the changes, wdiich is characteristic of several other wood-destroying 

 fungi. The growth in size of the white spots or cavities takes place 

 rapidly. The hyphffi grow out in all directions from the original 

 center, and as they do so the products of decomposition pass outward 

 likewise, passing along the tracheids faster than across them. After 

 a period the advancing hyphal masses of two adjacent holes meet in 

 the narrow lamella of unchanged Avood between the two. A quan- 

 tity of brown substance, representing decomposition products, has by 

 this time accumulated. It fills the tracheids and coats the hj^phje so 

 that these turn very dark, almost ])lack. Warm nitric' acid removes 

 these substances entirely, leaving the hypha' and wood almost color- 

 less. It is the opinion of the writer that this accumulation of the 

 products of decomposition ma}^ account for the fact that the destruc- 

 tion of the wood stops at this point, thus preventing the total 

 destruction of the wood substance. That this can not be true in all 

 cases is shown by the fact that many of the cavities join in the direc- 

 tion of the fibers, but in this instance it is probable that diffusion takes 

 place to more remote places. The mass of cellulose within the affected 

 areas consists of free fibers Avhich remain in place for a period and are 

 then gradually dissolved here and there, leaving an actual hole with a 

 lining of white fibers. 



In the newly invaded parts of a trunk the mycelium is colorless and 

 fills the tracheids completely. The Individual hypha- are somewhat 

 thick-walled and have numerous short branches which penetrate the 

 cell walls in all directions, leaving the characteristic figure 8 holes 

 described by Hartig and others. 



Here and there a second form of decomposition occurs in which 

 there is no reduction to cellulose. The process, as found in the spruce, 

 is essentially the same as described by Hartig. The secondary 

 lamella? arc gradually absorbed, leaving the primary lamella intact. 

 The wood araduallv changes into a mass of red-brown fibers which fall 

 apart at the slightest touch. 



The destruction of the wood takes place throughout the trunk, 

 including the heart and sapwood, and finally even the bark (see PI. 



