CHEMICAL AND PHYSICAL PROPERTIES. l^ 



flexible, highly hygroscopic and permeable by fluids ; lignified 

 woody substance is harder, stifter, and less liable to swell by the 

 absorption of water. 



2. There is a considerable quantity of water in freshly felled 

 wood — roughly, 45 per cent, of its weight — and this has 

 considerable influence on its technical qualities. 



The amount of water contained in ^\ood varies, however, with 

 the species, season, part of the tree, locality, &c. 



As regards species, broad-leaved wood generally contains 

 more water than coniferous wood. 



The season of felling has a great influence on the percentage 

 of water in wood, though it is dilflcult to say at what season 

 any wood will be wettest or driest, as this varies according 

 to species. The air-temperature, the degree of moisture of 

 the soil on which the tree was growing and the condition of the 

 roots, affect this question. In a general way, it may be said 

 that trees contain most water during early summer, and are 

 driest in autumn and late winter. According to E. Hartig's 

 investigations, the following table shows when the wood of 

 diff'erent species is wettest and driest : — 



As regards the part of the tree, in certain species and especially 

 conifers, the older inner wood is so dry that only the walls of 

 the woody elements contain water, and their lumiua none at all. 

 In other species, such as birch and oak, the inner part of 

 the wood is sometimes wetter and sometimes drier than the 

 outer portions, as the wetness of the sapwood varies greatly, 

 according to the season of the year. As a rule, wetness becomes 

 reduced towards the summit of the tree, and the roots contain 

 most water. 



