THE STEM AND ITS FUNCTIONS 



107 



cuts or sections. An ordinal y "cross cut," at right angles to the 

 length of the log, is known as a transverse section, and shows the 

 annual rings as a series of concentric circles, with the wood rays 

 running out from the center as narrow lines along the radii. 

 Whore the cut is longitudinal and made exactly along the radius 

 of the log, a 7'adial section results. This presents the annual 

 rings as vertical straight lines and the wood rays as horizontal 



..Large 

 Wood Rqij 



Spring 

 Vessels 



Annual 

 Ring 



Fig. 61. — A segment of an oak log. At the right, the block has been cut 

 radially, and above, transversely. At the left (the surface of the log) a portion 

 of the bast and corky bark has been removed, showing a tangential view of 

 the wood beneath. The wood rays are narrow sheets of tissue running along the 

 radii of the stem. On the radial face, one of them is shown split open, giving the 

 characteristic "silver grain" of oak wood. Between the large rays are many 

 small and narrow ones. 



stripes or markings. Where the rays are fairl}- wide, as in the 

 oak, these markings are prominent and furnish the much-prized 

 " silver grain " so readily seen in quartered oak. Other longitudi- 

 nal sections, which do not lie in a plane passing through the center 

 of the log, are known as tangential. If the structure is exactly 

 regular and the cut exactly true, the annual rings are here seen as 

 straight lines somewhat unequally distant, running up and down 

 along the wood. The irregularities' which almost always occur, 

 however, cause the rings in such a cut to appear as wavy lines 

 which produce the common "grain" of most wood surfaces. 

 The rays are very inconspicuous in a tangential section, for 

 only their cut ends are visible. The relations between these 



