DEFECTS IN THE ECONOMIC PROPERTIES OF WOOD. 149 



deviating from a vertical direction are excentric, e.g., all 

 branches and roots ; the pith is above the largest layers of 

 wood in coniferous branches (hyponasty) and below it in most 

 broadleaved branches (de Bary) * and in roots (epinasty). 

 Similarly all stems that, owing to wind or snow, are oblique 

 have excentric growth, i.e., the pith is nearer their upper 

 surface. Von Sachs and Hartig refer excentricity to pressure 

 or gravitation ; westerly winds exert pressure on a stem, and 

 this causes the formation of wide zones of wood on its eastern 

 side. The thicker bark on the upper surface of oblique stems 

 and on the southern and western sides of border trees influences 

 the formation of the wood, for the thicker the bark the less 

 wood is formed. 



Wood is fluted when its annual rings are crenate, that is 

 wavy, as in the wood of hornbeam, Fig. 18, and of yew. 

 Fluting may occur also in other species, and especially in 

 beech, underneath a large bough where the thickening of the 

 stem is less, while it is very vigorous on the two parallel sides 

 of the depression that is thus formed. 



There are two principal and several intermediate kinds of 

 crooked stems. A stem may be spiral or curved (sabre- 

 shaped) : the former defect occurs chiefly in the common, or 

 Scots, pine,t the latter in larch. 



Spiral stems are the less valuable the shorter the distance 

 between the windings of the spiral ; many entire stems are a 

 part only of a spiral. This defect in the common pine is said 

 by Mayr to be due to several causes, of which insufficient atmo- 

 spheric moisture is the chief. The tree is worstrshapen in 

 the driest part of its habitat, the south-west of Germany ; in 

 the moister and optimum climate of the species, West and 

 East Prussia, Poland, Courland and Livonia, it has a perfectly 

 straight stem ; so also outside its optimum climate, in its 

 most northerly habitat, in the moist climates of Norway, 

 Sweden, Finland and Russia. Even in less favourable parts 

 of Germany it is found that straightness of stem improves as 



* [Mayr says that all branch-wood resembles that of conifers in excentricity. 

 -Tr.] 



t [As Pinux xylrfixtri* grows all over Europe at different altitudes, and is 

 indigenous in England and Ireland as well as in Scotland, the term Scots pine 

 for it is a misnomer and its best name is "Common pine." Tr.] 



