WOODS AND THEIR DESTRUCTIVE FUNGI 437 



illustrated here can be detected is by their mycelia, consisting of 

 filaments of, usually, white cells, branching repeatedly by lateral rami- 

 fications, growing at their apices, lacing and interlacing, forming in 

 many places dense, felted masses. When they grow on the under 

 side of a plank, closely packed boards, and railroad-ties, they are often 

 similar in form to that shown in Fig. 5. So far as the decay of the 

 wood is concerned, the mycelia of the fungi is the most important 

 part. Though these filaments are small, ranging from 0*0004 to 0*002 

 of an inch in diameter, they are able to pierce the walls of the wood- 

 cells when softened by moisture, which many of them seem to gen- 

 erate to aid in their destructive work. 



The fungi, instead of propagating by visible seeds, only have mi- 

 croscopic spores, which are freely disseminated by the air to resting- 

 places. When proper conditions for germination occur, the spore 

 sends out a mycelium, which, by spreading over the under side of a 

 plank, as seen in Fig. 5, induces, sooner or later, the decomposition of 

 the structure of its host, to partly build up its own. 



Where it has once run over the wood in a dense growth, it destroys 

 its strength from one eighth to three fourths of an inch in depth, and 

 if the wood dries, cracks and crumbles to pieces (see Fig. 5) it forms 

 the so-called " dry rot " in timber, which is said to take place when the 

 wood is perfectly dry. This is a misconception, as it is impossible for 

 decay to commence without moisture, sufficient heat and access of air 

 to supply the amount of oxygen needed in the reduction of the tis- 

 sue to lower compounds. 



If the wood does not dry, the mycelia continues to grow until all 

 of the wood-cells are disorganized and fall to pieces, or, in other words, 

 completely rotted. In many cases, the mycelia works in the inner 

 portions of the timber, as explained later, and does not show exteriorly 

 until decay is well advanced ; this is especially true of larger timber. 



" Dry rot " was named from the effect produced, and not the cause, 

 to distinguish it from the so-called " wet rot." It has been an unfort- 

 unate designation, misleading many people, causing them to believe 

 that timber will rot when dry, and proper precautions have not been 

 taken to prevent decay, on the supposition that it would occur in any 

 event. 



The illustration in Fig. 5 is that of the mycelium of the Polypo- 

 rous radula (? Fr.) spreading on the under side of the plank of station- 

 platforms, which were destroyed in a year and a half to two years. 

 It is typical of a large number of the mycelia of the fungi growing in 

 similar conditions. One sees the same general appearance on lumber, 

 plank, and sawed railroad-ties, which are piled together without being 

 separated from each other by a small air-space. Hemlock inch boards 

 can be completely rotted through in six to eight weeks of July and 

 August weather, by the mycelia attacking both sides of the boards 

 when damp, and piled up without an air-space between each. Cargoes 



