•14 TECHNICAL l'K0I>EKTIE8 Ob' WOOD. 



The influence of the locality (especially the degree of damp- 

 ness of the soil and the factors of the locality which affect 

 the vital processes in plants) has not yet been thoroughly 

 studied as regards its effect on the amount of water in wood ; 

 but it appears as if the facts of trees being shallow or deep- 

 rooted, and possessing, or not, considerable powers of transpira- 

 tion, are chiefly concerned in the problem. 



3. The substances found in wood other than woody tissue 

 and water form only a small part of the general mass, and 

 only a few of them influence the technical properties of the 

 wood. 



The most important of these substances are protein, tannin 

 and other colouring matters, turpentine, starch, and the ash, or 

 residue of mineral substances after the wood has been burned. 



The protein substances, rich in nitrogen, are chiefly found in 

 young, unlignified wood, and especially in the cambium ; they 

 readih' decompose, and have hitherto been considered as the 

 chief accelerators of decay and rot in wood. Tannins are chiefly 

 found in the bark, but are rarely absent from the wood of any 

 species of tree. Their chief property influencing the technical 

 quality of wood is that they corrode iron when the latter is 

 used in contact with wood. Hence teak is preferred to oak 

 for the backing of plates in iron ships, as the tannin of 

 the oak corrodes and loosens the bolts which bind the 

 iron to the wood. Turpentine, which is found in varying 

 quantity in the wood of most conifers, and also of certain 

 tropical and semi-tropical broad-leaved species, influences the 

 technical qualities of wood in the highest degree. Turpentine 

 is chiefly found in the resin-ducts, but as these occur in the 

 medullary rays as well as among the tracheids, the whole of 

 the wood may become impregnated with turpentine, which after- 

 wards oxidizes into rosin, especially in the hcartwood and roots. 

 The quantity of rosin in wood also varies with the specific 

 gravity of the wood, depending on the greater or less develop- 

 ment of summer-wood, in or near which, most of the longitudinal 

 resin-ducts arc found. 



As regards starch, it is found that woody-tissues richest 

 in starch are most exposed to attacks of fungi and wood- 

 destroying insects. The ash- constituents of wood arc generally 



