48 



them have dissolved out the missing fibers and now fill the spaces. 

 Plate XI. fig. 3. represents a cross section of similarh^ attacked spruce 

 wood, showing several wood fibers of the spring wood at one side and 

 the gradual dissolution of adjoining ones, leaving only the more resist- 

 ant portions which lie free in the masses of hyphi^. These remaining 

 parts stain with phloroglucin and h^'drochloric acid, showing that they 

 are still lignified walls. Heartwood and sapwood of the spruce are 

 destroyed with equal rapidity. All parts become spongy, with the 

 exception of the resinous basal pieces of the branches, which resist the 

 attack of the fungus even after the whole trunk has been destroyed. 

 This resistance of the basal pieces of the branches is quite a common 

 feature in diseased trees attacked by several other fungi, notably 

 Polyporus schweinitzii^ but nowhere is it more striking than in this 

 instance. Text figure 3 shows such a branch piece as it appeared 

 immediately after pulling it from a dead standing tree. 



FRUITIXG OKGAX. 



After the mycelium has invaded the sapwood it grows out over the 

 bark, forming yellow felts. This takes place in the early part of the 

 summer, generally about Juh'. A few weeks later the small pores 

 begin to form. Certain hypha? of the sheet turn at right angles to 

 it and grow out at this angle, forming shallow pores. These are 

 almost round and are separated by very thin dissepiments. Fig. 2, 

 PL XV, is from a photograph of a spruce log, about the middle of Sep- 

 tember, almost natural size. As the season progresses the fungus 

 dies and splits up into smaller areas and some of the tubes become 

 inclined. No pores occur at the edge of the sheet, thus leaving a 

 fringe of sterile hyphae. This distinguishes this fungus from many 

 allied forms. The hymenial layer and the pores are generally straw 

 yellow, sometimes even more decidedly yellow, the color deepening 

 toward the latter part of the fall. The pores do not form until 

 December or January, and as a completely fruited fungus was col- 

 lected but once, its description will be deferred until more material 

 has been seen. 



The fruiting organ frequently develops in cracks and breaks formed 

 when a diseased tree is blown over. Fructification was induced in 

 many instances, as described above, by allowing' the air and moisture 

 to have access to completely decayed wood. 



AVhen Polyporus suhacidus grows in Northern forests on dead conif- 

 erous wood as a saproph3^te, its habit and action differs somewhat from 

 that described above. Inoculation experiments were made during the 

 summer to test how rapidly this fungus destroys sound wood. Dis- 

 eased wood from both dead and living trees was placed in holes l)ored 

 in healthy spruces, and the latter were labeled so as to be readily iden- 

 tified in later years. The amount of destruction which this fungus does 



