TIMBER FUNGI. 205 



and on wood that has been cut and worked up, occurring frequently on 

 bridges, railroad ties and the like, and causing prompt decay wherever 

 it has effected an entrance. The most conspicuous part of the fungus 

 is found frequently in the summer and fall on the diseased parts of 

 the tree or timber infested by it. It is particularly distinguished by the 

 formation of slender, dark-colored strings, consisting of compact myce- 

 lium, from which the fruiting parts arise. These hard, root-like strings 

 (called rhizomorphs) extend just beneath the surface of the ground, often 

 for a distance of severaF feet, and penetrate the roots of sound trees. 

 These rhizomorphs are a characteristic part of the fungus. They con- 

 stitute a most effective agency in the extension of the disease. 



"The symptoms are characteristic. The external symptoms, to be 

 observed especially in young specimens recently attacked, consist in a 

 change of the leaves to a pale, sickly color, and often the production 

 of short, stunted shoots. A still more marked symptom is the formation 

 of great quantities of resin, which flow downward through the injured 

 parts and out into the ground, resulting in the sticking together of the 

 roots and masses of dirt that have been penetrated by the resin. Passing 

 up a little way into the trunk, the cause of this is seen in the active 

 working of the fungus in the medullary rays and around the resin 

 canals, where apparently both cell contents and cell walls undergo de- 

 generation and partial conversion into resin. This flows downward, as 

 already stated, and also works laterally into the cambium, producing 

 great blisters in the younger parts where growth is going on, and also 

 resulting in the formation of unusually large resin canals. 



"As the disease advances the fungus continues to attack the tracheids 

 of the sound wood, and soon induces marked changes. Under its 

 influence the walls lose their lignified character, become softer, and give 

 the cellulose reaction, while the mycelium of the fungus penetrates and 

 fills the large cavities of the tracheids. 



"The whole inside of the trunk may finally become hollow for some 

 distance above the stump, its interior being filled with a loose, rotting 

 mass, penetrated by rhizomorph strings, and only becoming worse the 

 longer it stands. The disease having once reached this stage, there is 

 of course nothing to be done for the tree but to fell it as soon as 

 possible, and save whatever wood remains unaffected." 



Trametes, Polyporus, and Armillaria are quite distinctly parasitic, 

 though the last named does indulge in saprophytism. The following are 

 typical saprophytic, though occasionally attacking living trees through 

 wounds: 



(8) Polyporus vaporarius. Dry Rot, 



No mention of this species on any other tree than the Scotch pine 

 has been noted. It is a rather common wound parasite in Europe, but 

 affects more frequently the timbers which have been cut and piled in 

 a mill-yard, or placed unseasoned in a building. Its spores frequently 

 enter the cracks of barked logs lying in the woods, and when such 

 cracks are closed by soaking, as when the log is being transported by 

 water to the mill, the spores germinate and later the wood is found 

 to be infected with a snowy-white mycelium, and red or brown streaking 

 of the substance, in lines radiating from the crack in which the spore 

 germinated. The mycelium causes rotting and powdering of the wood. 



