i68 



THE STEM PROPER 



durable heartwood so prized by lumbermen. The heart- 

 wood is useful to the plant principally in giving strength 

 and firmness to the axis. It will now be seen why gird- 

 ling a stem, that is, chipping off a ring of the softer parts 



all round, will kill it, while 

 we often see vigorous and 

 healthy trees with the cen- 

 ter of the trunk entirely 

 hollow. 



237. Vertical Arrange- 

 ment. In studying the 

 vertical arrangement of 

 stems two sections are nec- 

 essary, a radial and a tan- 



311-313. Diagrams of sections of 

 timber: 311, cross section; 312, radial; 



313, tangential (from FiNCHOT, u.s. gentia! one. The former 



Dept. ofAgr.). 



^passes along the axis, split- 

 ting the stem into halves (Fig. 312); the latter cuts 

 between the axis and the perimeter, splitting off a segment 

 from one side (Fig. 313). 



238. The Graining of Timber. It is the medullary rays 

 that constitute the characteristic graining of different 

 woods. In a chip of red oak or chestnut from just beneath 



3*4- Tangential section of mountain ash, showing ends of the medullary rays. 



the bark their cut ends can be seen very distinctly with the 

 naked eye. Split a thicker chip of the same kind parallel 

 with the medullary rays and notice the difference, the 

 rays now appearing as silvery bands traversing the wood. 



