88 FORTY-FIBST ANNUAL REPORT ON THE 



dried or seasoned before use, tlie decay commenced is checked and 

 will not revive until the wood again becomes moist from external 

 causes. On the contrary, if such wood is put into structures while 

 damp and unseasoned, then painted or confined where the moisture is 

 retained, the decay will continue, the rapidity depending upon the 

 continued amount of damp and warm weather or equivalent con- 

 ditions. This is commonly and erroneously called " dry rot." Decay 

 of dry wood can not take place without moisture. 



It is well established by numerous proofs that seasoned woods last 

 in all conditions of service where it is unfavorable for the growth 

 of fungi, and decay in all conditions where they can grow, unless the 

 timber is judiciously treated. The propagation of fungi uj)on timber 

 may be either by germination of spores, which are thrown off b}' 

 thousands when in fructification and disseminated by the air, or by 

 revival of mycelium already on or in the wood. 



Besides the ever-present spores of a fungus or its mycelium in 

 timber, three essential conditions in combination are necessary for the 

 decay of wood, or in other words, the growth of a fungus. 



First. Moisture, either external or internal. 



Second. A temperature between 40° and 120° Fahr., 75° to 90° 

 being the most favorable for the maximum growth of fungi. 



Third. A small amount of air, still or nearly quiet. Free circula- 

 tion or winds check the growth of mycelium when in direct contact 

 with it. 



When wood must be exjDOsed to these three conditions, sooner or 

 later, according to its structure and cell contents, fungi grow and 

 destroy it as a result of a natural law of their growth. Therefore, to 

 j)rotect seasoned wood from decay, the combination mentioned must 

 be prevented from taking place by rejecting either one of the three 

 elements; or, if that is impossible, an antisej)tic or preservative must 

 be used to prevent the growth of any fungi. This brief statement 

 comprehends, both theoretically and practically, what is necessary to 

 be done to jDreserve timber structures from decay, but to reduce the 

 principles to j)ractice, so as to meet all conditions of service which 

 may occur, requires a knowledge of the structure of the particular 

 wood, its cell contents, size of stick to be used and care in seasoning. 

 Also a knowledge of the special fungus or fungi attacking the species 

 of wood, and the value and proper use of preservatives and 

 antiseptics. 



Species of fungi which I have found upon specific looods lohen used as 

 railroad ties or in bridges. 



The tungi peculiar to white oak, Quercus alba, L., are Polyporus 



