4 TIMBER AND SOME OF ITS DISEASES. [CHAP. 



which mark the " grain " are continuations of the lines 

 which mark the annual rings, as shown in Fig. 2, 



FIG. 2. Portion of segment of wood from a log such as Fig. i, supposed to be slightly 

 magnified, a, annual ring ; m, medullary rays ; m', the same in vertical section ; 

 c, the boundary line between one annual ring and another; sn, autumn wood; sp, 

 spring wood ;/, the pith. 



which represents on a larger scale a segment such as 

 could be cut from a log in the way described. It is 



