116 TRANSACTIONS OF THE [,1AN. 4, 



The chemical composition of wood is not practically alike, as 

 iccontly stated, but differs even in the sap-wood and heart-wood 

 of the same species. Some of the woods have compounds in 

 their cells, easily induced to decompose and start the wood tis- 

 {-uc, while othci-s have different comjiounds, requiring iuducing 

 :i;i('i!ts of greater intensities to begin dccav. 



A study of tiie gi'owlh and functions of the fungi enables ns 

 1() understand why. in jiractical ojierations. it is 8o diflicult to 

 ]»i('vent large timber from decaying internally, while I'cmaining 

 sound upon the exterior. The spoi-es so abundant in the atmo- 

 sphere find ready lodgment in the checks of the timber before it 

 is thoroughly seat-oncd. 'J'hcseare inclosed by boarding, painting, 

 or exterior tieatment, or even exjioscd to tiie sun so as to dry 

 the outside and thus prevent the eva]ioration of the internal 

 moisture, and the spoi-es germinate and either grow a mycelium 

 <)!• set np the feini en (active action, destroying tiie inside of the 

 limber, leaving a mere shell outside. Tiiis was the case with 

 "the painted Howe truss bridges, erected for the western I'ail- 

 loads ; many of them rotting in four to five years. Roads which 

 were too poor to paint the bridges the first year, found they histed 

 longer. These were very instructive lessons to me, and, in 1873, 

 •when designing and erecting a sei-ies of long i-ailroad trestles; I 

 made my posts six by eight inches, using two, set three inches 

 apart. This allowed them to season, and gave me about the 

 same factor of safety as one ten by ten, which would not season, 

 but would rot in six to seven years. And my tiestles are still in use. 



The exterior coatings intended to ]ireserve the Niclutlson i)ave- 

 nicnt blocks, was about the most effective means which could 

 have been used to destroy them. ]\Iany other faihires of ti'eated 

 timber are due to this same cause — namely — inclosure of the 

 s])()]'es, theii- growth, and fei'mentation. 



I have liei-e a i)iece of wood, used for the slieathing of freight 

 cai's, which has already undergone initial decay. Its cells con- 

 iain the germs to destroy it. A coat of paint on the outside, 

 iind a little moisture inside the car, would complete the decay. 

 <Jars sheathed iioi-izontally retain moistui-e in the tongueing and 

 grooving longer tiian those vertically sheathed, and in conse- 

 <iuence they ai'c destroyed sooner by the growth of fungus, seem- 

 ingly a trifiing affaii", but really of great financiid imjjortance. 



Some eft'oi'ls to pi-eserve certain timber for some i)laces have 

 1)ccn successful ; but attempts to preserve all kinds and sizes on 

 Ihc same goieial ])lan, have ivsulted in many costly failures, and 

 huge corjiorat ions have lost faith in such effoi'ts !o ])rolong the 

 .«eivice of the wood. Why some succeeded and others failed, 

 Imrdly excited a query, mucii less an investigation; and hence 

 i:o(»d and jioor methods were equally condemned. 



