82 



and through wounds. The mycelium flourishes in both heartwood 

 and sapwood of the Spruces, the Fir. and Tamarack, and is confined to 

 the heartwood in the Pine. It grows up and down the trunk from 

 the point of infection, reaching into the root system and extending 

 into the larger branches of the top. Affected trees may remain 

 standing in the forest for many years until some more violent storm 

 breaks the trunk at a weak point. The Avood of the trunk is never 

 destroyed completely, as in the case of the two fungi described above. 

 In the most advanced stages of decay some fibers of unchanged wood 

 are to be found. The extent of their presence varies with the tree. 



DESTRUCTIOX OF SPRUCE WOOD. 



The first effect noticed when the mycelium grows in the wood of 

 either of the Spruces is a change in color from the light straw yellow 

 of the normal wood to a light purplish gray closely approaching the 

 color indicated on the Milton Bradle}^ Color Scale as Neutral Gray No. 1. 

 Very soon this gra^' deepens to a red brown, the gray remaining as an 

 outer ring surrounding the portions of red-brown wood. Small black 

 lines appear scattered here and there through the red wood. These lines 

 are present throughout an annual ring and extend longitudinally in the 

 direction of the wood fibers for a distance of -V to gV of an inch (0..5 to 1 

 millimeter). Gradually the black lines disappear and here and there 

 small white areas appear (PI. VI, fig. 1). The central portion of each 

 area is absorbed and small holes are formed, which have white linings 

 of loose fibers. The holes are at some distance from one another and 

 are generally arranged in rows corresponding to the annual rings. 

 Where the latter are very wide there may be a row of holes in each ring. 

 The holes generalh' have their centers within the summer wood of the 

 annual ring, but as the}^ increase in size portions of the spring Avood 

 of that particular ring, as well as the spring wood of the folio wing- 

 ring, are included. The holes have a more or less spherical shape, 

 which soon changes to a more or less elongated form, the greatest 

 diameter extending radially. PI. X, fig. 2, shows a cross section of 

 a piece of wood at an early stage of the destruction. Some of the 

 holes at this period are filled Avith a mass of Avhite fibers, so that there is 

 practicalh' no hole. The outlines shown in fig. 2 of PI. X represent 

 the outer limiting line of the white fibers, and the dotted lines (Avhere 

 present) indicate where the actual cavit}^ begins. As the groAvth of 

 the m3xelium progresses, the holes increase in size and their walls 

 approach one another until only a narrow lamella is left (PI. X, fig. 8). 



A large number of holes appear between the original ones, and in 

 the final stages there is practically no wood left except the narrow 

 walls separating two holes (PI. X, fig. 3, and PI. VI, fig. 2). Adjoin- 

 ing cavities rarely, if CA^er, unite to form a larger one in a lateral 

 direction. They often unite at their upper and lower ends, forming 



