246 Double Cross-Grain 



causes, first, the numbering of the rings was done without comparison 

 between the two series, and secondly, the fainter rings did not stand out 

 so clearly in the sticks of the longitudinal series, with the result that a 

 certain number of them escaped observation. However, the spacing of 

 the rings and the phase of inclination shown by the grain clearly indicate 

 that the 30th to 60th ring inclusive of the transverse series correspond 

 with those numbered from 24 to 50 in the longitudinal series. 



The diagram illustrating the longitudinal series (Fig. 4) shows that 

 the curves which indicate the course of the grain in each stick agree 

 together very closely as to form, a fact foreshadowed by the longitudinal 

 parallel zones to be seen on the surface of a radial board, and demonstrate 

 that in a radial plane the inclination of the grain alternates between 

 left-handed and right-handed with the growth of the tree. 



On reading off from Fig. 4 the position of each maximum inclination 

 of the grain with reference to the rings, for the successive sticks of the 

 longitudinal series it is seen that the position of each corresponding 

 maximum inclination may remain the same through the series, for 

 example, the one occurring between the 40th and 41st rings, or else it may 

 vary within a range of two or three rings, or finally, as in the last two 

 periods, the position of a maximum inclination of the grain may pass, on 

 being traced through successive transverse levels, more to the exterior 

 or vice versa, according to whether the series is examined from the one 

 end or the other. 



Thus in Shorea robusta it is apparent that though the periods are 

 structurally continuous, their development at different transverse levels 

 in the same radial plane is not necessarily simultaneous, though it usually 

 is so. 



From the curves for sticks 1 to 9 (Fig. 4) it is seen that some of the 

 earlier periods do not retain their identity throughout the series; the 

 period comprised between the 12th and 20th rings in stick 6 fades away 

 in sticks 5 to 1, its place being taken by a fresh period. The board, un- 

 fortunately, was not long enough to extend beyond this transitional 

 region to where the new period would be fully established. 



In some of the other species this fading away of some periods and 

 the increase in the prominence of others was of much more frequent 

 occurrence, and constituted one of the chief causes of lack of corre- 

 spondence shown by successive curves of a series whether transverse 

 or longitudinal. 



That the appearance of this transitional region is not due to errors 

 in the determination of the inclination of the grain is proved by the 



