J. F. Martlby -233 



examined of the changes in the course of the grain during the life of the 

 tree. 



In order that the individual curves of a series should be more readily 

 comparable among themselves the growth -rings were plotted for all the 

 curves according to their width along a stick of intermediate length. 

 In the longitudinal series this procedure produced no distortion of the 

 curves since in all the species examined the width of the rings remained 

 practically constant through the series, but in the transverse series, on 

 the other hand, a distortion of some of the curves would be caused 

 where the growth of the tree had been excentric. This distortion however 

 will not affect the value of the curves for comparing changes in the 

 inclination of the grain. 



In order to test the reliability of the results obtained by this method 

 of investigating the course of the grain, recourse was had to an elabora- 

 tion of the method of radial fracture already described under the head 

 of "Preliminary Investigations" as the most convenient method for 

 demonstrating double cross-grain. 



For checking the longitudinal series of curves, a radial board, if 

 possible adjacent to the one which supplied the material from which the 

 changes in the course of the grain in the longitudinal direction had been 

 derived, was sawn transversely into a number of sticks an inch broad. 

 For ease in subsequent comparison several of the more prominent rings 

 were inked in on the corresponding transverse surfaces of the sticks. 

 Each stick was then split radially, the direction of the split being made 

 in the same sense in each stick. When the sticks were placed in sequence 

 side by side a series of curved fractures was shown which, though not 

 always identical in form, corresponded very closely with the longitudinal 

 series of curves of the same species. 



Prior to describing the course of the grain in the different species, it 

 is advisable to mention the errors to which the method of investigation 

 is subject and to estimate their probable effect on the results obtained. 



The use made of the rings as an index of contemporaneity has 

 already been discussed. The distinctness with which the individual 

 rings could be followed round the discs and through the longitudinal 

 series reduced errors in the numbering of the rings to a negligible 

 minimum in all except the transverse series of Gmelina arhorea. 



In the actual measurement of the inclination of the grain on the 

 slips repeated tests showed that errors from this source were not likelv 

 to have exceeded one degree. 



Where the radial board had not been sawn parallel to the axis of 



