26 TECHNICAL PROPERTIKS OF WOOD. 



gravity of spruce and larch iu the Alps, with a short growing 

 season and intense light, when compared with wood of these 

 species from the plains ; the high specific gravity of oakwood 

 grown on warm aspects compared with that from cold localities ; 

 the low specific gravity of sessile oak on poor, sandy soils ; the 

 fine-ringed sprucewood from the higher Alps and the extreme 

 north of Europe ; the porous wood produced, especially hy the 

 pedunculate oak and elm, when trees are grown iu very wet 

 situations ; the high specific gravity of some of the hroadcr 

 annual zones of conifers when the trees arc isolated and their 

 crowns fully exposed to light. 



Although it follows from the above that there must be a 

 considerable difference from year to year and from place to place 

 in the amount of summer-wood, the question arises whether the 

 breadth of the ring will alone suffice to decide the specific 

 gravity of a particular wood ? This question can be answered 

 only after a study of the different groups of woods. As regards 

 woods which are ring-pored, it may be laid down that quick- 

 grown, wide-ringed wood is denser than narrow-ringed wood, 

 provided that G millimeters (} inch) is not exceeded. {Vide 

 Plate I.) 



[As a rule, broad-leaved woods of the same species become heavier 

 when grown more to the south, so that sessile oakwood may be much 

 heavier from rroveuce tluui from Normandy. — Tu.] 



For wood with evenly distributed pores, the breadth of the 

 rings is no indication of comparative density, the difference 

 between the spring- and summer-wood being so slight. 

 R. Hartig states that the breadth of the annual zones in beecli- 

 •\vood has no influence on its specific gravity, which de])ends on 

 the age of the tree. During youth heavier wood is formed and 

 during maturity lighter wood, as the larger the crown of the tree, 

 the greater the lumina of the woody elements through which the 

 water passes from the roots to the foliage. If, then, superior 

 beechwood is produced in good localities, it is usually because, 

 in such places the rotation is shorter, and the wood felled when 

 it is younger than in inferior localities. 



Regarding conifers, long experience has shown that, in the 

 majority of cases, narrow rings imply heavier wood than broad 



