STEMS, KOOTS, AND LEAVES 



87. 



The wood rays are more numerous than in young shoots and 

 vary greatly in length and width according to their position and 

 the time of formation. This is due to the fact that as the wood 

 increases in circumference new rays are started from the cam- 

 bium at various points year by year. The new rays supply a 



Transverse 



Transvers 



Annual 



ring 



Radial section Oblique -tangential section 

 a b 



Quarter -sawing 

 c 



Straight grain 

 d 



avy grain 

 f 



FIG. 48. Various cuts of wood drawn to show the grain and other 

 structural features 



Consult the text for an explanation of these figures 



larger food-storage system for the tree, which, with the disap- 

 pearance of the pith and cortex, comes to be lodged more and 

 more in the wood rays and wood parenchyma of the wood 

 cylinder. The pith usually disappears very early and is marked 

 by a dark spot in the center of the tree. 



The above tissues and tissue layers have a very different 

 appearance when observed in wood blocks or in thin sections cut in 



