46 



itself differs markedlj" in different trees. This difference appears to be 

 due somewhat to the rapidity with which the solution of the libers 

 takes place. As a rule, the wood in the early stages of the attack has 

 numerous black spots scattered throughout its mass (PL XI Y, tig. 1). 

 These black spots are surrounded by a white circle before long, and 

 somewhat later disappear entirely, leaving very much larger Avhite 

 spots. The wood around the spots is now straw-^^ellow in color and 

 begins to look somewhat frayed, as if groups of wood fibers were sepa- 

 rating readily from the rest. A tendency for the different annual rings 

 to separate now becomes very marked (PL XIV, fig. 1, at the right), and 

 a log of spruce wood at this stage can be split into concentric rings by 

 mere pounding. Gradually the number of white spots increases. In 

 one form of decay the white spots are confined almost entirely to the 

 summer wood. The newly formed spots are also in the summer wood, 

 and before ver}^ long all the summer w^ood of every ring, including 

 also some of the adjacent spring wood of that ring, has turned white. 

 This stage of decomposition is shown very well in PL XIV, fig. 2, a 

 longitudinal section of a spruce log, and in PL XV, fig. 1, a cross 

 section of the same log. It will be noted that the change to the white 

 masses nowhere passes from the summer wood of one ring to the 

 spring wood of the adjoining ring. There is evidently some agent, 

 presumably of a chemical nature, which confines the solvent action of 

 the fungus mycelium to the summer wood and prevents it from 

 attacking the spring wood. It may be recalled here that where a 

 similar change takes place in the spruce wood, induced b}- the mjxelium 

 of Trametes pini forma ahietls (PL X, fig. 2) both summer and spring 

 wood were changed. This localized action of the dissolving agent takes 

 place with such regularity and in so many different ways, depending 

 upon the kind of fungus attacking the wood, that it suggests the 

 presence of specifically distinct dissolving agents, enzymes, perchance, 

 for each fungvis. 



In the second form of deca}^ the appearance of the white spots is 

 limited to the summer wood in the same way as above described. The 

 white spots do not increase in number so rapidh^ and consequently do 

 not form the white bands spoken of. Changes take place within the 

 wood cells of the spring wood, which give to them a very light and 

 porous nature. A cubic inch (16. •I'''') of such wood completely decayed 

 weighs but 1.3 grams (sound spruce wood weighs 5.52 grams). 



The mycelium of the fungus spreads through the individual tracheids 

 after entering the tree, and collects in spots here and there. Solution 

 of the wood cells begins around these centers, which at this time appear 

 dark brown or black. They are the black spots referred to above. 

 The change which takes place around these centers consists in a solution 

 of the hadromal and the other lignin constituents of the cell walls, 

 leaving the pure cellulose fibers free from one another. These con- 



