228 Double Cross-Grain 



tracings of the fractures obtained are reproduced in Fig. 1. An examina- 

 tion of the tracings shows that there are all types of gradation from the 

 approximately straight grain of Albizzia procera to the uniform type of 

 the double cross-grain characteristic of Shorea robusta. 



The differences in the character of the cross-grain of the various 

 species appear to be of a quantitative rather than of a qualitative nature, 

 depending on the degree of regularity in the changes in the inclination 

 of the grain, on the average radial distance between the successive 

 right-handed and left-handed phases and on the a . erage angle included 

 between the maximum left-handed and right-handed inclinations of 

 the grain. 



The splitting of a radial stick provides a ready means of demon- 

 strating changes of inclination in the grain for a very limited portion 

 of the trunk, but in order to obtain a satisfactory insight into the 

 variations in the inclination of the grain it is essential to know what the 

 appearance of the grain would be like on the surface of the woody 

 cylinder at successive intervals during the life of the tree. 



The presence of clearly denned " growth -rings " greatly facilitated 

 this investigation for, on the assumption that they delineated tissues 

 produced at the same time, these rings supplied the necessary time unit 

 without which it would have been impossible to proceed. 



In order to obtain a general idea of the course of the grain in a drum 

 use was made of these rings in the case of Xylia dolabriformis by splitting 

 successive collars from off the disc at every fifth ring, and by careful 

 planing of a radial board tangentially to the rings. In both cases the 

 inclination of the grain was noted on the successively exposed surfaces. 

 It was not possible to make detailed records of the variations seen 

 in the inclination of the grain, but the general impression obtained was 

 that there were alternate right-handed and left-handed phases of 

 inclination throughout the drum and that the conformation of the grain 

 on the surface of the woody cylinder was at all times of the type already 

 described under Group II, since, in the radial plane, the grain was often 

 serpentine, its general direction alternating between left-handed and 

 right-handed, and because around any ring in the transverse disc, the 

 grain was never uniformly inclined although its inclination alternated 

 with growth between wholly right-handed and wholly left-handed. 



Before proceeding with the detailed method of investigation, a 

 digression is necessary in criticism of the assumption that the rings of 

 these Indian timbers are of the nature of growth-rings. 



In dicotyledonous trees, native to temperate climates, the rings are 



