46 ECONOMIC WOODS OF THE UNITED STATES 



DeBakt, A.: Comparative Anatomy, pp. 507-511. 



Munch, Ernst: Ueber krankhafte Kernbildung, Naturw. Zeitsohrift fur 



Forst- und Landwirtschaft, 8. Jahrgang, 1910, pp. 533-547; 553-569. 

 Nordlingeb, H.. Die Technischen Eigenschaften der Holzer, Stuttgart, 



1860, pp. 28^0. 



GRAIN AND TEXTURE 



Grain is a general term used in reference to the arrangement 

 or direction of the wood elements and to the relative width of 

 the growth rings. To have specific meaning it is essential that 

 it be qualified. The kinds of grain commonly described are fine, 

 coarse, even, uneven, rough, smooth, straight, cross, spiral, twisted, 

 wavy, curly, mottled, landscape, bird's-eye, gnarly, and silver. 



Coarse grain applies to woods of rapid growth, i.e., it denotes 

 wide rings; fine grain, to woods of slow growth. Even and uneven 

 apply respectively to regularity or irregularity of the growth rings ; 

 rough and smooth, to the manner in which wood works under tools. 

 Straight grain, as applied to a tree, occurs when the wood ele- 

 ments are parallel to the axis of growth; as applied to a board, 

 when the radial and tangential planes of structure are parallel 

 to its length. Sawn boards or timbers are often cross-grained 

 even when cut from straight-grained logs while straight-grained 

 pieces may be split from spiral-grained trees. The strength of 

 a piece of timber, particularly in bending, rapidly weakens as the 

 plane of its fibres deviates from a direction parallel to its length. 

 On this account split timber is usually stronger than when sawn, 

 a fact made use of in wood-working. For instance, billets for 

 handles and blocks for telegraph-insulator pegs are invariably 

 split. 



It is not uncommon in any tree, and usual in many cases, for 

 the wood elements to be arranged spirally about the central axis. 

 The spiral may run to the right or left, but the direction is usually 

 fairly constant within a species. Various theories have been 

 advanced to explain the phenomenon of spiral growth or torsion. 

 The one most commonly accepted considers the obliquity of the 

 fibres a method of accommodating the increase in length of the 

 cells after their formation in the cambium. There seems to be 

 ground for suspecting that wind may have an influence on this 

 spiral development. For instance, trees of Larix americana have 

 been observed which, though straight-grained while young, had 



