26 



the .shape of broad, irregular liancls. which extend across the rings of 

 growth. The point.s at which these white areas appear and the direc- 

 tion which they take do not seem to be controlled by any particular 

 factor, for they are exceedingl}^ irregular. The areas are shown in 

 PI. Ill, which represents a radial view of a spruce log in the earlj^ 

 stages of attack ])y the mycelium. The very fine white lines which 

 are visible near the center of the log, extending across the annual 

 rings, are of a different character from the white areas spoken of. It 

 will be noted that in the white areas the parallel lines which indicate 

 the summer wood are ver}' distinct. A microscopic examination of a 

 white area shows that at this point the cells of the wood are com- 

 pletely filled with fine hypha\ which form a dense mass within that 

 area. Mixed in with the mycelium are the granules of an amorphous 

 substance, readily soluble in alcohol, which is evidently resin. This, 

 together with the mycelium, gives the white appearance to the spots. 

 As the summer tracheids have a very small lumen, they have compara- 

 tively little mycelium, which accounts for their being visible as lines 

 extending through the areas. The size of an ai'ea is thus dependent 

 upon the distance to which the mycelium has grown, and probably 

 varies from time to time. It is suggested that the smaller areas are 

 also the ones most recentl}' invaded. At this stage of the decomposi- 

 tion the mass of the wood is already very brittle. Here and there 

 cracks have appeared in the walls of the wood cells wherever a hypha 

 has passed through them. Some tracheids appear like sieves because 

 of the numerous holes. The changes subsequent to this stage of 

 decomposition consist essentially in a carbonizing of the wood and the 

 formation of the sheets of mycelium. The former change is one proba- 

 bly induced by some ferment, the nature of which it is the intention to 

 discuss more fulh' in another report. The cells of the wood gradually 

 show more and more cracks and fissures, and the diameter of the walls 

 decreases about half. The main shrinkage takes place in the secondarj" 

 lamella^. The fissures which appear in the spring wood usually 

 emanate from the holes formed by hypha?. The outline of these holes 

 is irregular, but approaches a circle in form. In the secondary wall a 

 fissure is soon formed which extends diagonally from left to right 

 across the cell. Viewed from the top there are apparently two 

 fissures, but these can readily be shown to belong to the secondary 

 lamella? of adjoining cells. The fissures never extend into the primary 

 lamella?. Various stages of such fissures are shown at PI. X, fig. 4. 

 In the bordered pits at first two and later four fissures are visible in 

 the secondary ring, which, as Hartig has surmised,^ are probably 

 brought about b}' drving. Here and there (PI. X, fig. -I, c) a hypha 

 has passed directh' through a bordered pit and in its passage has 



^ Hartig, Robert. Zersetzungserscheinungen des Holzes, etc. 



