224 



DOUBLE CROSS-GRAIN. 



By J. F. MARTLEY. 



(With Plate XIII and 11 text-figures.) 



Theke is a certain amount of ambiguity in the meaning of the term 

 cross-grain as applied to wood owing to it being used to describe con- 

 ditions of grain which are similar in appearance though due to different 

 causes. 



The simplest use of the term is in its application to a plank sawn 

 obliquely to the longitudinal axis of a straight grained log. A similar 

 condition of the grain can be seen in planks, especially in the outer ones, 

 which have been sawn from logs of considerable taper. 



A more logical use of the term is in the description of planks sawn 

 from a torse or spiral-grained log, for in this case it is impossible to saw 

 a plank without cutting across the grain. 



There is still a further type of cross-grain, seen in many timbers native 

 to hot climates, which might be called interlocked or double cross-grain, 

 the investigation of which forms the subject of the present paper. 



This grain can often be recognised by a characteristic banded appear- 

 ance on radial surfaces, due to differences in the reflection of light from 

 a number of zones parallel to the longitudinal axis of the trunk. When 

 such a wood is planed, it is at once evident that the grain in alternate 

 zones is inclined in opposite directions. 



This variation in the inclination of the grain can also be demonstrated 

 by making successive tangential splits in a narrow stick sawn transversely 

 off the end of a radial board, when it will be found that the inclination 

 of the grain swings alternately to the left and right of the straight. 



In the absence of any specific investigation, the simple spiral grain 

 of torse wood suggested that the grain of these exotic timbers is of the 

 nature of a double spiral, the inclination of the grain alternating with the 

 growth of the tree between a left-handed and a right-handed spiral. It 

 was on this supposition that Professor Groom based the explanation of 

 the warping and twisting phenomena of the dipterocarpous wood called 

 Yang(i). 



