82 



and through wounds. The ni^x-clium tlourishes in both hcartwood 

 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 wood of the trunk is never 

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

 In the most advanced stages of decaj^ some fibers of unchanged wood 

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



DESTRUCTION OF SPRUCE AVOOD. 



The first effect noticed when the mj^celium 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 Bradley Color Scale as Neutral Gray No. 1. 

 Ver}^ soon this gray 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 ^V of an inch (0.5 to 1 

 millimeter). Gradualh^ the black lines disappear and here and there 

 small white areas appear (Fl. VI, tig. 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 they increase in size portions of the spring wood 

 of that particular ring, as well as the spring wood of the following- 

 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. Fl. 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 with a mass of white fibers, so that there is 

 practicall}' no hole. The outlines shown in fig. 2 of Fl. X represent 

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

 present) indicate where the actual cavity begins. As the growth of 

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

 approach one another until only a narrow lamella is left (Fl. X, fig. 3). 



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 (Fl. X, fig. 3, and Fl. VI, fig. 2). Adjoin- 

 ing cavities rarely, if ever, unite to form a larger one in a lateral 

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



